# Code and Formats
source: https://developer.mastercard.com/eligibility-api/documentation/code-and-formats/index.md

Use this page when a request fails and you need the quickest answer to "what error did I receive?" The Eligibility API, widget flows, and gateway responses all use a standard error structure with HTTP status codes, reason codes, and recovery guidance. Start here to identify the issue before you dive into the deeper reference pages.

### Common error categories {#common-error-categories}

* HTTP status codes and generic response payloads
* Eligibility API reason codes
* Widget API reason codes
* Invalid request, authentication, and authorization failures

<br />

### Reference links {#reference-links}

* [Generic Code and Formats](https://developer.mastercard.com/eligibility-api/documentation/code-and-formats/generic-code-and-formats/index.md)
* [Eligibility Error Codes](https://developer.mastercard.com/eligibility-api/documentation/code-and-formats/eligibility-error-codes/index.md)
* [Widget Error Codes](https://developer.mastercard.com/eligibility-api/documentation/code-and-formats/widget-error-codes/index.md)

## Next Steps {#next-steps}

* Use the [Testing](https://developer.mastercard.com/eligibility-api/documentation/testing/index.md) guide to reproduce and validate the error scenarios documented here against Sandbox.
* Review the [API Reference](https://developer.mastercard.com/eligibility-api/documentation/api-reference/index.md) to confirm the request fields tied to each reason code.
* If an error persists after following the resolution steps, contact [Support](https://developer.mastercard.com/eligibility-api/documentation/support/index.md).