OAuth2.0 token strange behaviour (Invalid Credentials 401)

Question

Usually, Google OAuth2.0 mechanism is working great.

1. The user confirms permission to access Google account with selected scopes.
2. The refresh token is

Answer 1

I had this problem when I tried experimenting with changing the redirect url in google console and then updating my json credentials file on server. I had to clear the session variables before starting afresh. So in your project just do this once:

session_start(); //starts a session
session_unset(); //flushes out all the contents previously set

Remember to remove the session_unset() after dry running it once.