RefreshError ('invalid_grant: Token has been expired or revoked.') Google API

About a week ago I set up an application on google. Now when I tri and run:

SCOPES = ['https://www.googleapis.com/auth/gmail.readonly']
creds = None
if os.path.exists('token.pickle'):
     with open(self.CREDENTIALS_PATH+self.conjoiner+'token.pickle', 'rb') as token:
        creds = pickle.load(token)
        if not creds or not creds.valid:
            if creds and creds.expired and creds.refresh_token:
                creds.refresh(Request()) ##error here

I get the following error:

Exception has occurred: RefreshError
('invalid_grant: Token has been expired or revoked.', {'error': 'invalid_grant', 'error_description': 'Token has been expired or revoked.'})

What could be the problem?

token.pickle contains the access token and refresh token for your application.

>Token has been expired or revoked.'

Means that the refersh token in this file is no longer working this can be caused by servral reasons.

1. the user revoked your access
2. The user has authorized your access token more then 50 times and this is the oldest token and was there for expired
3. the refresh token hasn't been used in six months
4. The project is still in the testing phase, and there for the refresh token will be expired after seven days.

All of the above information can be found in Oauth2 expirationdocumentation

the solution for options 1- 3 is to simply delete the token.pickle file and request authorization of the user again.

For number four you should go to google developer console under the Oauth2 consent screen and set your application to production. Then your refresh token will stop expiring. Then you can delete the token.pickle and you wont have this issue again.

None of the answers here or there quite got me back on track, but the resolution was quite simple (and obscure):

• Delete your google token .pickle files and re-run your script.

In my case I'm using a Julia wrapper around Google's Sheets API called GoogleSheets. The (two) files in that case start with google_sheets_token and are stored in ~/.julia/config/google_sheets/ along with the credentials.json file.

I don't know why there were two pickle files (maybe for two auth scopes, though to be fair much of Google's authentication schemes are mysterious to me) but deleting both of them causes the next run of the script to throw up the OAuth prompt in a browser window, and all is well again.

They seem to expire fairly often and there are various confident theories about why. But the reason seems to change roughly as often as they expire so just deleting them each time seems to be the most reliable fix.