invalid_callback_request

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 → 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 fragments—ensure the provider uses query/body for server-side callbacks.
• Multiple redirects (including HTTP → 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>