What causes invalid_grant in OAuth?

Usually an expired authorization code, reused code, PKCE verifier mismatch, or rotated refresh token.

How do I fix redirect_uri_mismatch?

The redirect_uri in your request must exactly match the registered URI in your provider dashboard — including protocol, trailing slash, and path.

invalid_grant. redirect_uri mismatch. PKCE misconfiguration. OAuthFixer identifies the likely cause — and generates the provider fix.

Paste your error, select your provider and flow. Get the exact config change, dashboard step, and SDK snippet to fix it.

Paste your OAuth error

Your provider ← Select your provider above to see the exact dashboard steps and SDK fix

Your flow

You might also need

    ⚡CORSFixer
Test live CORS preflight and get the middleware fix🔍JWT Debugger
Decode and validate JWTs — flags expired tokens and weak algorithms🔒HeadersFixer
Scan security headers and get stack-specific fixes
  

Done with this tool?
20 HTTP checks before you ship — security, CORS, cache, redirects, staging.
Pre-Launch Checklist →

About OAuthFixer

What errors does OAuthFixer diagnose?

OAuthFixer identifies comn OAuth 2.0 and OIDC errors including invalid_grant, redirect_uri_mismatch, invalid_client, access_denied, invalid_scope, unauthorized_client, and PKCE misconfigurations.

What is invalid_grant?

invalid_grant means the authorization code or refresh token is no longer valid. Common causes include an expired code, a code that was already used, a PKCE verifier mismatch, or a refresh token that was rotated or revoked.

What is PKCE and why is it required?

PKCE (Proof Key for Code Exchange) is a security extension for the authorization code flow. It prevents authorization code interception attacks by binding the code to a verifier known only to the client. Most providers require it for public clients (SPAs and mobile apps).

Which providers does OAuthFixer support?

OAuthFixer generates provider-specific dashboard steps and SDK config for Auth0, Okta, Cognito, Google, Microsoft, and Generic OIDC providers.