> ## 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.

# Card sessions

> Public error codes for Card sessions API endpoints

All error responses follow the standard [error format](/api-reference/errors/error-handling).
Validation errors (422) and rate limit errors (429) apply to all endpoints and are documented in the [Error Handling guide](/api-reference/errors/error-handling).

| Code | Status | Detail |
| - | - | - |
| `card_session_purchase_required` | 400 | purchase is required for a card the user saved. The user approves that purchase. |
| `invalid_value` | 400 | The information you entered isn't valid. Please check it and try again. |
| `unauthenticated` | 401 | Authentication is required. |
| `card_use_not_permitted` | 403 | This agent isn't allowed to use the user's saved cards. |
| `forbidden` | 403 | You do not have permission to perform this action. |
| `card_not_found` | 404 | Card not found. |
| `card_session_not_found` | 404 | Card session not found. |
| `already_exists` | 409 | The resource already exists. |
| `card_not_active` | 409 | The card is not active. |
| `card_session_already_claimed` | 409 | The card session was already claimed. Create a new session. |
| `card_session_approval_lapsed` | 409 | The user's approval is no longer usable. Create a new session. |
| `card_session_declined` | 409 | The user declined this purchase. |
| `card_session_expired` | 409 | The card session expired before it was claimed. Create a new session. |
| `card_session_pending_approval` | 409 | The user hasn't approved this purchase yet. Keep polling the session. |
| `conflict` | 409 | The request conflicts with the current resource state. |
| `rate_limited` | 429 | Too many requests. Please try again later. |
| `server_error` | 500 | Something went wrong. |
| `bad_gateway` | 502 | We couldn't complete that request because one of Natural's services returned an unexpected response. Please try again. |
| `bad_gateway` | 502 | Natural could not complete the request because one of its services returned an unexpected response. Try again. |
| `card_session_provider_unavailable` | 503 | Couldn't issue the card credential. Try again later. |
| `card_sessions_unavailable` | 503 | Card sessions aren't available for this card in this environment. |
| `service_unavailable` | 503 | The service is temporarily unavailable. |