# Source: https://www.better-auth.com/llms.txt/docs/reference/errors/invalid_callback_request.md

# invalid_callback_request

The callback request is invalid.



## What is it?

This error is thrown during the OAuth callback when the incoming request cannot be parsed or is missing
required fields.

## Common Causes

* Query or body parameters were stripped by a reverse proxy, CDN, or framework rewrite.
* Double-encoding or improper URL encoding of parameters causes parsing to fail.
* Callback URL mismatch at the provider triggers an intermediate redirect that drops parameters.
* Middleware or route grouping sends the request to a different handler than intended.
* Very long URLs get truncated by an intermediary (rare but possible with some proxies).

## How to resolve

### Verify callback method and parameters

* Ensure your provider is configured to use the method your route expects (commonly GET with query parameters for Authorization Code flow).
* Confirm the callback includes required parameters (e.g., `code` and `state` for standard OAuth flows).

### Preserve query/body through infrastructure

* Check that reverse proxies (Vercel, Cloudflare, Nginx) and app rewrites forward the full query string and request body intact.
* If middleware intercepts or rewrites the callback, make sure it forwards all parameters without modification.

### Debug locally

* In DevTools â Network, inspect the callback request and verify parameters are present and well-formed.
* Compare dev/staging/prod credentials to ensure there are no environment differences causing different flows or endpoints.

### Edge cases to consider

* Mobile/WebView or deep-link flows can drop query parameters during handoff.
* Some providers can return parameters in fragments; your server will not receive fragmentsâensure the provider uses query/body for server-side callbacks.
* Multiple redirects (including HTTP â HTTPS) can lose parameters if not configured correctly.

<Callout type="info">
  Callback parameters are normally handled automatically by Better Auth. If this error appears, it often
  indicates manual access to the `/api/auth/callback` route, a proxy/redirect that stripped parameters,
  or an integration mismatch. Double-check provider settings and infrastructure rewrites to ensure the
  full request reaches the callback unchanged.
</Callout>