intermittent error while calling GMAIL API - "The caller does not have permission"

Question

getting this error intermittently

HttpError 403 when requesting https://www.googleapis.com/discovery/v1/apis/gmail/v1/rest returned "The caller does not have permission"

It works sometimes and other times it doesn't. I see the same issue on the oauth2 playground

this is my code -

googlecredentials = GoogleCredentials(
    access_token=None,
    client_id='xxx',
    client_secret='xxxx',
    refresh_token='xxxx',
    token_expiry=None,
    token_uri="https://www.googleapis.com/oauth2/v3/token", 
    user_agent='Python client library'
)

service = build('gmail', 'v1', credentials=googlecredentials)

results = service.users().labels().list(userId='me').execute()
labels = results.get('labels', [])
response = service.users().messages().list(userId='me', q='subject:FDA').execute()
print(response)

Answer 1

I was also facing this issue came very recently. I have been using GMAIL API for more than a year now and I have never faced this issue. I don't know if there is an issue from our side or Gmail changed their policy of usage. But, regardless I did manage to find the solution for it. The main issue that I was having was my creds (google credentials in your case) was getting expired and each time it was expired I had to refresh them. So, a simple solution would be to just refresh them.

if not creds or not creds.valid:
    if creds and creds.expired and creds.refresh_token:
        creds.refresh(Request())

My native language is python so I have written the code in the same language but you can head over here and see something similar in your native language

Thank you.