FAQ & Troubleshooting

1. I'm getting an "Unauthorized" error

This usually means you are posting an incorrect or misspelled API key. Double-check that your key is correct and that it is formatted properly in the Authorization header.

Example of a failed auth response:

{
  "error": "werkzeug.exceptions.Unauthorized",
  "message": "The server could not verify that you are authorized to access the URL requested."
}

[!TIP] Make sure you include the trailing colon after your API key when using Basic Auth (e.g., YOUR_API_KEY:). The colon separates the username from the empty password.

2. I'm getting an "Unsupported payment method" error

Each payment method must be activated on your account before it can be used. If you attempt to use an inactive method, the API returns a 400 Bad Request:

{
  "error": "werkzeug.exceptions.BadRequest",
  "message": "The requested payment method is not active for this merchant."
}

[!NOTE] Contact your Cost+ account manager or enable the payment method in the admin portal under Settings > Payment Methods.

3. Which test card numbers can I use?

See the Testing Your Integration page for a full list of test card numbers for both Shift4 and Rapyd payment providers, including cards that simulate successful and failed transactions.

4. How are webhook retries handled?

If your webhook endpoint does not respond with a 2xx status code, Cost+ will retry delivery:

• Up to 10 retries, spaced 2 minutes apart.
• The first attempt times out after 4 seconds.
• Subsequent retries time out after 10 seconds.

[!WARNING] If all 10 retries fail, the webhook event is marked as failed and will not be retried again. Make sure your endpoint responds quickly and returns a 200 status code.

For full details on webhook configuration and payload formats, see the Webhooks guide.