> This page is for Documentation, version Integration guides (default).
> For other versions, use one of these documentation indexes:
> - Integration guides (default): https://avalara.ferndocs.com/docs/integration-guides/llms.txt
> - Refactor guides: https://avalara.ferndocs.com/docs/refactor-guides/llms.txt
> - Get certified: https://avalara.ferndocs.com/docs/get-certified/llms.txt
> - Agent to Agent (A2A): https://avalara.ferndocs.com/docs/agent-to-agent-a2a/llms.txt
> - AI use cases: https://avalara.ferndocs.com/docs/ai-use-cases/llms.txt
> - API versioning: https://avalara.ferndocs.com/docs/api-versioning/llms.txt

> For clean Markdown of any page, append .md to the page URL.
> For a complete documentation index, see https://avalara.ferndocs.com/llms.txt.
> For AI client integration (Claude Code, Cursor, etc.), connect to the MCP server at https://avalara.ferndocs.com/_mcp/server.

# Error handling

We’ve designed the [AvaTax error messages](https://developer.avalara.com/avatax/errors/) to tell you what went wrong during an API call, what you can do about it, and how to proceed.

When an AvaTax API call produces an error, it responds using the standard [HTTP error response codes](https://en.wikipedia.org/wiki/List_of_HTTP_status_codes). Response codes between 400 and 499 are called **Client Errors**, and they indicate a mistake in an API call. Response codes between 500 and 599 refer to internal errors within AvaTax itself. Each internal error is automatically logged and reported to our development team for triage.

If your program gets an HTTP response code between 400 and 499, here’s how to proceed:

* Parse the error message using a JSON parsing engine.
* Display the summary of the error to the user.
* Link the user to the documentation page that explains the error.
* Allow the user to make a change to their request, or retry their action.

For example, if an AvaTax API call fails to include authentication credentials, the user will see the error message [AuthenticationIncomplete](https://developer.avalara.com/avatax/errors/AuthenticationIncomplete).

[Previous](https://developer.avalara.com/avatax-dm-combined-erp/common-setup/authentication/test-authentication)

[Next](https://developer.avalara.com/avatax-dm-combined-erp/common-setup/error-messages/reasonable-errors)

> **Note**
>
> Part of the **AvaTax and ECM** integration guide. [Open the full "Error handling" milestone on Avalara](https://developer.avalara.com/avatax-dm-combined-erp/common-setup/) to see every page in this section.