How should my code handle a 402 from the Casafari API?

Treat a 402 payment_required from the self-serve platform as a pause: pass the upgrade_url to a person, poll the payment link until it completes, then retry the request.

Errors are application/problem+json, and each error type has a page at https://platform.casafari.com/errors/<code>, such as https://platform.casafari.com/errors/payment_required.

1. Read the upgrade_url from the error; the same link is in a Link header with rel="payment".
2. Show the link to a person, who opens it and pays. Your code cannot pay.
3. Poll GET https://platform.casafari.com/v1/account/payment-links/{id} about every 5 seconds until the status is completed. Polling costs 0 units.
4. Retry the original request.

For the same flow over MCP, see when units run out. For other errors, see REST errors and retries and which errors to retry.