> ## Documentation Index > Fetch the complete documentation index at: https://docs.natural.com/llms.txt > Use this file to discover all available pages before exploring further. > ## Agent Instructions > When building application code, use `@naturalpay/sdk` for TypeScript or `naturalpay` for Python. > When operating Natural directly for a user, use the payments MCP at `https://mcp.natural.com`. > When searching Natural documentation, use the docs MCP at `https://docs.natural.com/mcp`. > Use the Natural CLI for terminal and CI automation. > Use REST only for unsupported languages or when the user explicitly requests raw HTTP. > Start integration development and testing in the sandbox. Do not use production unless the user explicitly requests it. > For sandbox requests that require `customerPartyId`, list customers first. Reuse only the intended fixture; otherwise create a customer. > REST and SDK amounts use integer minor units. Payments MCP amounts use decimal strings with a required currency code. # Sandbox: Fulfill a payment request > Fulfill an open payment request addressed to your test payer Pays a request addressed to your [test payer](/api-reference/sandbox/fixtures#request-a-payment) from the fixture's funded wallet. ## OpenAPI ````yaml POST /simulations/payment-requests/{paymentRequestId}/fulfill openapi: 3.1.1 info: title: Natural API version: 0.2.0 description: >- Natural's payments API for autonomous agents. **Base URL:** `https://api.natural.com` AI agents, including coding agents, should prefer the hosted MCP server at `https://mcp.natural.com` when an MCP-aware host runs the agent, the Natural CLI for terminal/CI workflows, and the official SDKs for application runtimes they own. Use direct HTTP only for explicit low-level integrations, unsupported SDK gaps, or infrastructure work where REST is required. For support: support@natural.com servers: - url: https://api.natural.com description: Production security: [] tags: - name: Agents description: Agent management - name: Customers description: Customer management - name: Invitation Links description: Shareable links that offer your agents to customers - name: Payments description: Payment management - name: Transactions description: Transaction activity and history - name: Transfers description: Deposits and withdrawals - name: PaymentRequests description: Payment request management - name: Approvals description: Approval review - name: Invitations description: Party invitation management - name: Parties description: Party and organization management - name: Wallets description: Wallet management - name: External Accounts description: Linked external bank accounts - name: External Parties description: Third parties with whom you transact over Direct - name: External Party Accounts description: Banking details belonging to external parties not on Natural - name: ACH description: Make ACH payments to external party accounts - name: API Keys description: API key management - name: Agent Keys description: Agent key management - name: Webhooks description: Webhook endpoint management - name: Events description: Webhook event log - name: Simulations description: Sandbox-only simulation controls paths: /simulations/payment-requests/{paymentRequestId}/fulfill: post: tags: - Simulations summary: Fulfill payment request as test payer description: Fulfill an open payment request addressed to your test payer operationId: simulations.fulfillPaymentRequest parameters: - name: paymentRequestId in: path required: true schema: type: string pattern: ^prq_[0-9a-f]{32}$ description: Payment request controlled by the fixture. - name: Idempotency-Key in: header required: true schema: type: string maxLength: 255 description: >- Unique key for safely retrying a request without creating duplicates. - name: X-Agent-ID in: header required: false deprecated: true schema: anyOf: - type: string maxLength: 36 pattern: ^agt_[0-9a-f]{32}$ - type: 'null' description: >- Deprecated: agent identity comes from the credential. Sending this header with a party API key or user credential returns 403 agent_credential_required. - name: X-Instance-ID in: header required: false schema: anyOf: - type: string maxLength: 1024 - type: 'null' description: >- Caller-chosen identifier for the agent run, session, or conversation, required when an agent moves money. responses: '200': description: Successful Response content: application/json: schema: type: object properties: data: type: object properties: type: type: string enum: - payment id: type: string pattern: ^pay_[0-9a-f]{32}$ attributes: type: object properties: amount: type: integer description: Amount in cents. currency: type: string description: Currency code. status: enum: - CREATED - PROCESSING - PENDING_CLAIM - IN_REVIEW - COMPLETED - FAILED - RETURNED - APPROVAL_DENIED - CANCELED type: string description: Payment status. description: anyOf: - type: string - type: 'null' description: Payment description. tags: type: object propertyNames: type: string additionalProperties: type: string description: >- Metadata visible to anyone who can read the resource. createdAt: type: string description: When this payment was created. updatedAt: anyOf: - type: string - type: 'null' description: When this payment was last updated. required: - amount - currency - status - description - tags - createdAt - updatedAt additionalProperties: false title: PaymentAttributes relationships: type: object properties: sender: type: object properties: data: anyOf: - type: object properties: type: type: string enum: - party id: type: string pattern: ^pty_[0-9a-f]{32}$ required: - type - id additionalProperties: false title: ResourceIdentifier description: Related resource identifier. - type: 'null' required: - data additionalProperties: false title: NullableToOneRelationship description: >- Party that initiated the payment, when the sender is on Natural. senderAgent: type: object properties: data: anyOf: - type: object properties: type: type: string enum: - agent id: type: string pattern: ^agt_[0-9a-f]{32}$ required: - type - id additionalProperties: false title: ResourceIdentifier description: Related resource identifier. - type: 'null' required: - data additionalProperties: false title: NullableToOneRelationship description: >- Sending agent, or null when the payment was not sent by an agent. recipient: type: object properties: data: anyOf: - type: object properties: type: type: string enum: - party id: type: string pattern: ^pty_[0-9a-f]{32}$ required: - type - id additionalProperties: false title: ResourceIdentifier description: Related resource identifier. - type: 'null' required: - data additionalProperties: false title: NullableToOneRelationship description: Recipient party for this payment, when known. recipientAgent: type: object properties: data: anyOf: - type: object properties: type: type: string enum: - agent id: type: string pattern: ^agt_[0-9a-f]{32}$ required: - type - id additionalProperties: false title: ResourceIdentifier description: Related resource identifier. - type: 'null' required: - data additionalProperties: false title: NullableToOneRelationship description: >- Recipient agent, or null unless addressed by agent ID or agent handle. transaction: type: object properties: data: anyOf: - type: object properties: type: type: string enum: - transaction id: type: string required: - type - id additionalProperties: false title: ResourceIdentifier description: Related resource identifier. - type: 'null' required: - data additionalProperties: false title: NullableToOneRelationship description: >- Sender-side transaction for this payment, when available. paymentRequest: type: object properties: data: anyOf: - type: object properties: type: type: string enum: - paymentRequest id: type: string pattern: ^prq_[0-9a-f]{32}$ required: - type - id additionalProperties: false title: ResourceIdentifier description: Related resource identifier. - type: 'null' required: - data additionalProperties: false title: NullableToOneRelationship description: >- Payment request that produced this payment, when applicable. required: - sender - senderAgent - recipient - recipientAgent - transaction - paymentRequest additionalProperties: false title: PaymentRelationships required: - type - id - attributes - relationships additionalProperties: false title: PaymentResource required: - data additionalProperties: false title: PaymentResponse examples: default: summary: Default value: data: type: payment id: pay_550e8400e29b41d4a71644665544000d attributes: amount: 2500 currency: USD status: PROCESSING description: Invoice 7 tags: {} createdAt: '2026-01-04T15:30:00Z' updatedAt: '2026-01-04T15:35:00Z' relationships: sender: data: type: party id: pty_019cd1798d617f65a79cb965dda9eac3 senderAgent: data: null recipient: data: type: party id: pty_550e8400e29b41d4a71644665544000a recipientAgent: data: null transaction: data: type: transaction id: txn_550e8400e29b41d4a71644665544000b paymentRequest: data: type: paymentRequest id: prq_550e8400e29b41d4a71644665544000c headers: X-RateLimit-Limit: description: Maximum requests allowed per window. schema: type: integer X-RateLimit-Remaining: description: Requests remaining in current window. schema: type: integer X-RateLimit-Reset: description: Unix timestamp when rate limit resets. schema: type: integer '400': description: Validation Error content: application/json: schema: type: object properties: errors: type: array minItems: 1 items: type: object properties: code: type: string description: Stable lower-snake-case public error code. detail: type: string description: Safe user-facing error detail. status: type: string description: HTTP status code as a string. source: type: object description: Location of the invalid request value. properties: pointer: type: string description: JSON Pointer to the invalid request value. parameter: type: string description: Name of the invalid query parameter. header: type: string description: Name of the invalid request header. additionalProperties: false meta: type: object description: >- Additional error context, including support and provider details when available. properties: supportId: type: string description: Request/support ID for troubleshooting. connectionStatus: type: string enum: - login_required - disconnected description: >- External account connection state when the error is repairable by relinking. provider: type: object description: Provider error details, when available. properties: name: type: string enum: - plaid description: Provider that returned the underlying error. errorCode: type: string description: Provider error code, when available. errorType: type: string description: Provider error type, when available. requestId: type: string description: Provider request ID for troubleshooting. required: - name additionalProperties: false required: - supportId additionalProperties: false required: - code - detail - status - meta additionalProperties: false required: - errors additionalProperties: false examples: default: summary: Default value: errors: - code: invalid_value detail: >- The information you entered isn't valid. Please check it and try again. status: '400' meta: supportId: req_a1b2c3d4e5f6 '401': description: Unauthorized content: application/json: schema: type: object properties: errors: type: array minItems: 1 items: type: object properties: code: type: string description: Stable lower-snake-case public error code. detail: type: string description: Safe user-facing error detail. status: type: string description: HTTP status code as a string. source: type: object description: Location of the invalid request value. properties: pointer: type: string description: JSON Pointer to the invalid request value. parameter: type: string description: Name of the invalid query parameter. header: type: string description: Name of the invalid request header. additionalProperties: false meta: type: object description: >- Additional error context, including support and provider details when available. properties: supportId: type: string description: Request/support ID for troubleshooting. connectionStatus: type: string enum: - login_required - disconnected description: >- External account connection state when the error is repairable by relinking. provider: type: object description: Provider error details, when available. properties: name: type: string enum: - plaid description: Provider that returned the underlying error. errorCode: type: string description: Provider error code, when available. errorType: type: string description: Provider error type, when available. requestId: type: string description: Provider request ID for troubleshooting. required: - name additionalProperties: false required: - supportId additionalProperties: false required: - code - detail - status - meta additionalProperties: false required: - errors additionalProperties: false examples: default: summary: Default value: errors: - code: unauthenticated detail: Authentication is required. status: '401' meta: supportId: req_a1b2c3d4e5f6 '403': description: Forbidden content: application/json: schema: type: object properties: errors: type: array minItems: 1 items: type: object properties: code: type: string description: Stable lower-snake-case public error code. detail: type: string description: Safe user-facing error detail. status: type: string description: HTTP status code as a string. source: type: object description: Location of the invalid request value. properties: pointer: type: string description: JSON Pointer to the invalid request value. parameter: type: string description: Name of the invalid query parameter. header: type: string description: Name of the invalid request header. additionalProperties: false meta: type: object description: >- Additional error context, including support and provider details when available. properties: supportId: type: string description: Request/support ID for troubleshooting. connectionStatus: type: string enum: - login_required - disconnected description: >- External account connection state when the error is repairable by relinking. provider: type: object description: Provider error details, when available. properties: name: type: string enum: - plaid description: Provider that returned the underlying error. errorCode: type: string description: Provider error code, when available. errorType: type: string description: Provider error type, when available. requestId: type: string description: Provider request ID for troubleshooting. required: - name additionalProperties: false required: - supportId additionalProperties: false required: - code - detail - status - meta additionalProperties: false required: - errors additionalProperties: false examples: default: summary: Default value: errors: - code: forbidden detail: You do not have permission to perform this action. status: '403' meta: supportId: req_a1b2c3d4e5f6 '404': description: >- Not Found. Returned when the resource does not exist, or when it exists but is not accessible to your account. The two cases are intentionally indistinguishable, so that resource IDs cannot be enumerated by probing. content: application/json: schema: type: object properties: errors: type: array minItems: 1 items: type: object properties: code: type: string description: Stable lower-snake-case public error code. detail: type: string description: Safe user-facing error detail. status: type: string description: HTTP status code as a string. source: type: object description: Location of the invalid request value. properties: pointer: type: string description: JSON Pointer to the invalid request value. parameter: type: string description: Name of the invalid query parameter. header: type: string description: Name of the invalid request header. additionalProperties: false meta: type: object description: >- Additional error context, including support and provider details when available. properties: supportId: type: string description: Request/support ID for troubleshooting. connectionStatus: type: string enum: - login_required - disconnected description: >- External account connection state when the error is repairable by relinking. provider: type: object description: Provider error details, when available. properties: name: type: string enum: - plaid description: Provider that returned the underlying error. errorCode: type: string description: Provider error code, when available. errorType: type: string description: Provider error type, when available. requestId: type: string description: Provider request ID for troubleshooting. required: - name additionalProperties: false required: - supportId additionalProperties: false required: - code - detail - status - meta additionalProperties: false required: - errors additionalProperties: false examples: default: summary: Default value: errors: - code: not_found detail: The requested resource was not found. status: '404' meta: supportId: req_a1b2c3d4e5f6 '408': description: '408' content: application/json: schema: oneOf: - type: object properties: defined: const: true code: type: string enum: - SANDBOX_NOT_READY status: const: 408 message: type: string default: >- The deposit was accepted, but its Transfer is not visible yet. Retry with the same Idempotency-Key. data: type: object properties: reason: type: string enum: - SANDBOX_NOT_READY required: - reason additionalProperties: false title: SandboxNotReadyErrorData required: - defined - code - status - message - data - type: object properties: defined: const: false code: type: string status: type: number message: type: string data: {} required: - defined - code - status - message '409': description: Conflict content: application/json: schema: type: object properties: errors: type: array minItems: 1 items: type: object properties: code: type: string description: Stable lower-snake-case public error code. detail: type: string description: Safe user-facing error detail. status: type: string description: HTTP status code as a string. source: type: object description: Location of the invalid request value. properties: pointer: type: string description: JSON Pointer to the invalid request value. parameter: type: string description: Name of the invalid query parameter. header: type: string description: Name of the invalid request header. additionalProperties: false meta: type: object description: >- Additional error context, including support and provider details when available. properties: supportId: type: string description: Request/support ID for troubleshooting. connectionStatus: type: string enum: - login_required - disconnected description: >- External account connection state when the error is repairable by relinking. provider: type: object description: Provider error details, when available. properties: name: type: string enum: - plaid description: Provider that returned the underlying error. errorCode: type: string description: Provider error code, when available. errorType: type: string description: Provider error type, when available. requestId: type: string description: Provider request ID for troubleshooting. required: - name additionalProperties: false required: - supportId additionalProperties: false required: - code - detail - status - meta additionalProperties: false required: - errors additionalProperties: false examples: default: summary: Default value: errors: - code: conflict detail: The request conflicts with the current resource state. status: '409' meta: supportId: req_a1b2c3d4e5f6 '422': description: Validation Error content: application/json: schema: type: object properties: errors: type: array minItems: 1 items: type: object properties: code: type: string description: Stable lower-snake-case public error code. detail: type: string description: Safe user-facing error detail. status: type: string description: HTTP status code as a string. source: type: object description: Location of the invalid request value. properties: pointer: type: string description: JSON Pointer to the invalid request value. parameter: type: string description: Name of the invalid query parameter. header: type: string description: Name of the invalid request header. additionalProperties: false meta: type: object description: >- Additional error context, including support and provider details when available. properties: supportId: type: string description: Request/support ID for troubleshooting. connectionStatus: type: string enum: - login_required - disconnected description: >- External account connection state when the error is repairable by relinking. provider: type: object description: Provider error details, when available. properties: name: type: string enum: - plaid description: Provider that returned the underlying error. errorCode: type: string description: Provider error code, when available. errorType: type: string description: Provider error type, when available. requestId: type: string description: Provider request ID for troubleshooting. required: - name additionalProperties: false required: - supportId additionalProperties: false required: - code - detail - status - meta additionalProperties: false required: - errors additionalProperties: false examples: default: summary: Default value: errors: - code: invalid_value detail: >- The information you entered isn't valid. Please check it and try again. status: '422' source: pointer: /data/attributes/email meta: supportId: req_a1b2c3d4e5f6 '428': description: Precondition Required content: application/json: schema: type: object properties: errors: type: array minItems: 1 items: type: object properties: code: type: string description: Stable lower-snake-case public error code. detail: type: string description: Safe user-facing error detail. status: type: string description: HTTP status code as a string. source: type: object description: Location of the invalid request value. properties: pointer: type: string description: JSON Pointer to the invalid request value. parameter: type: string description: Name of the invalid query parameter. header: type: string description: Name of the invalid request header. additionalProperties: false meta: type: object description: >- Additional error context, including support and provider details when available. properties: supportId: type: string description: Request/support ID for troubleshooting. connectionStatus: type: string enum: - login_required - disconnected description: >- External account connection state when the error is repairable by relinking. provider: type: object description: Provider error details, when available. properties: name: type: string enum: - plaid description: Provider that returned the underlying error. errorCode: type: string description: Provider error code, when available. errorType: type: string description: Provider error type, when available. requestId: type: string description: Provider request ID for troubleshooting. required: - name additionalProperties: false required: - supportId additionalProperties: false required: - code - detail - status - meta additionalProperties: false required: - errors additionalProperties: false examples: default: summary: Default value: errors: - code: mfa_required detail: MFA verification required status: '428' meta: supportId: req_a1b2c3d4e5f6 '429': description: Too Many Requests content: application/json: schema: type: object properties: errors: type: array minItems: 1 items: type: object properties: code: type: string description: Stable lower-snake-case public error code. detail: type: string description: Safe user-facing error detail. status: type: string description: HTTP status code as a string. source: type: object description: Location of the invalid request value. properties: pointer: type: string description: JSON Pointer to the invalid request value. parameter: type: string description: Name of the invalid query parameter. header: type: string description: Name of the invalid request header. additionalProperties: false meta: type: object description: >- Additional error context, including support and provider details when available. properties: supportId: type: string description: Request/support ID for troubleshooting. connectionStatus: type: string enum: - login_required - disconnected description: >- External account connection state when the error is repairable by relinking. provider: type: object description: Provider error details, when available. properties: name: type: string enum: - plaid description: Provider that returned the underlying error. errorCode: type: string description: Provider error code, when available. errorType: type: string description: Provider error type, when available. requestId: type: string description: Provider request ID for troubleshooting. required: - name additionalProperties: false required: - supportId additionalProperties: false required: - code - detail - status - meta additionalProperties: false required: - errors additionalProperties: false examples: default: summary: Default value: errors: - code: rate_limited detail: Too many requests. Please try again later. status: '429' meta: supportId: req_a1b2c3d4e5f6 headers: Retry-After: description: Seconds to wait before retrying. schema: type: integer X-RateLimit-Limit: description: Maximum requests allowed per window. schema: type: integer X-RateLimit-Remaining: description: Requests remaining in current window. schema: type: integer X-RateLimit-Reset: description: Unix timestamp when rate limit resets. schema: type: integer '500': description: Internal Server Error content: application/json: schema: type: object properties: errors: type: array minItems: 1 items: type: object properties: code: type: string description: Stable lower-snake-case public error code. detail: type: string description: Safe user-facing error detail. status: type: string description: HTTP status code as a string. source: type: object description: Location of the invalid request value. properties: pointer: type: string description: JSON Pointer to the invalid request value. parameter: type: string description: Name of the invalid query parameter. header: type: string description: Name of the invalid request header. additionalProperties: false meta: type: object description: >- Additional error context, including support and provider details when available. properties: supportId: type: string description: Request/support ID for troubleshooting. connectionStatus: type: string enum: - login_required - disconnected description: >- External account connection state when the error is repairable by relinking. provider: type: object description: Provider error details, when available. properties: name: type: string enum: - plaid description: Provider that returned the underlying error. errorCode: type: string description: Provider error code, when available. errorType: type: string description: Provider error type, when available. requestId: type: string description: Provider request ID for troubleshooting. required: - name additionalProperties: false required: - supportId additionalProperties: false required: - code - detail - status - meta additionalProperties: false required: - errors additionalProperties: false examples: default: summary: Default value: errors: - code: server_error detail: Something went wrong. status: '500' meta: supportId: req_a1b2c3d4e5f6 '501': description: Not Implemented content: application/json: schema: type: object properties: errors: type: array minItems: 1 items: type: object properties: code: type: string description: Stable lower-snake-case public error code. detail: type: string description: Safe user-facing error detail. status: type: string description: HTTP status code as a string. source: type: object description: Location of the invalid request value. properties: pointer: type: string description: JSON Pointer to the invalid request value. parameter: type: string description: Name of the invalid query parameter. header: type: string description: Name of the invalid request header. additionalProperties: false meta: type: object description: >- Additional error context, including support and provider details when available. properties: supportId: type: string description: Request/support ID for troubleshooting. connectionStatus: type: string enum: - login_required - disconnected description: >- External account connection state when the error is repairable by relinking. provider: type: object description: Provider error details, when available. properties: name: type: string enum: - plaid description: Provider that returned the underlying error. errorCode: type: string description: Provider error code, when available. errorType: type: string description: Provider error type, when available. requestId: type: string description: Provider request ID for troubleshooting. required: - name additionalProperties: false required: - supportId additionalProperties: false required: - code - detail - status - meta additionalProperties: false required: - errors additionalProperties: false examples: default: summary: Default value: errors: - code: not_implemented detail: This operation is not available. status: '501' meta: supportId: req_a1b2c3d4e5f6 '502': description: Bad Gateway content: application/json: schema: type: object properties: errors: type: array minItems: 1 items: type: object properties: code: type: string description: Stable lower-snake-case public error code. detail: type: string description: Safe user-facing error detail. status: type: string description: HTTP status code as a string. source: type: object description: Location of the invalid request value. properties: pointer: type: string description: JSON Pointer to the invalid request value. parameter: type: string description: Name of the invalid query parameter. header: type: string description: Name of the invalid request header. additionalProperties: false meta: type: object description: >- Additional error context, including support and provider details when available. properties: supportId: type: string description: Request/support ID for troubleshooting. connectionStatus: type: string enum: - login_required - disconnected description: >- External account connection state when the error is repairable by relinking. provider: type: object description: Provider error details, when available. properties: name: type: string enum: - plaid description: Provider that returned the underlying error. errorCode: type: string description: Provider error code, when available. errorType: type: string description: Provider error type, when available. requestId: type: string description: Provider request ID for troubleshooting. required: - name additionalProperties: false required: - supportId additionalProperties: false required: - code - detail - status - meta additionalProperties: false required: - errors additionalProperties: false examples: default: summary: Default value: errors: - code: bad_gateway detail: >- We couldn't complete that request because one of Natural's services returned an unexpected response. Please try again. status: '502' meta: supportId: req_a1b2c3d4e5f6 '503': description: Service Unavailable content: application/json: schema: type: object properties: errors: type: array minItems: 1 items: type: object properties: code: type: string description: Stable lower-snake-case public error code. detail: type: string description: Safe user-facing error detail. status: type: string description: HTTP status code as a string. source: type: object description: Location of the invalid request value. properties: pointer: type: string description: JSON Pointer to the invalid request value. parameter: type: string description: Name of the invalid query parameter. header: type: string description: Name of the invalid request header. additionalProperties: false meta: type: object description: >- Additional error context, including support and provider details when available. properties: supportId: type: string description: Request/support ID for troubleshooting. connectionStatus: type: string enum: - login_required - disconnected description: >- External account connection state when the error is repairable by relinking. provider: type: object description: Provider error details, when available. properties: name: type: string enum: - plaid description: Provider that returned the underlying error. errorCode: type: string description: Provider error code, when available. errorType: type: string description: Provider error type, when available. requestId: type: string description: Provider request ID for troubleshooting. required: - name additionalProperties: false required: - supportId additionalProperties: false required: - code - detail - status - meta additionalProperties: false required: - errors additionalProperties: false examples: default: summary: Default value: errors: - code: service_unavailable detail: The service is temporarily unavailable. status: '503' meta: supportId: req_a1b2c3d4e5f6 security: - HTTPBearer: [] servers: - url: https://api.sandbox.natural.com description: Sandbox components: securitySchemes: HTTPBearer: type: http scheme: bearer description: >- Bearer authentication: send your API key, agent key, or OAuth access token as `Authorization: Bearer `. ````