PKCE verification failed
What it means
The code_verifier does not hash to the code_challenge sent at sign-in.
Fix
Use base64url (no padding) SHA-256 of the exact verifier, and keep the verifier per attempt.
Check it with smart-doctor
Run your login and smart-doctor ranks this cause against the others, with the evidence it found.
npx smart-doctor check my-profileAlready have the server’s error? Explain it without running anything.
npx smart-doctor explain '{"error":"invalid_grant"}'