Fix OAuth Errors on Auth0 — PKCE, redirect_uri, invalid_grant

Auth0 tenants reject tokens when redirect_uri does not exactly match an Allowed Callback URL—including trailing slashes and custom schemes. PKCE public clients must send code_verifier that matches the original challenge; rotation errors surface as invalid_grant.

Use Auth0’s debugger and OAuthFixer’s provider hints to compare authorization requests with Application settings. Enable refresh token rotation only when your server stores refresh tokens securely.

Also see invalid_grant and PKCE required.