No callback URL

What is it?

This error occurs during the OAuth flow when the request reaches your /api/auth/callback endpoint but the state data does not contain a callback URL. Better Auth stores metadata in state when the flow starts, including where to redirect after a successful sign-in/link. If that URL is missing at callback time, we cannot safely continue.

Common Causes

• The OAuth flow was not started via Better Auth APIs, so the state payload never included a callback URL.
• A reverse proxy, CDN, or middleware altered the flow, causing the app to read a different or empty state.

How to resolve

Start the flow through Better Auth

• Always initiate OAuth using Better Auth's built-in methods so state is generated with the needed fields.