For information on specific errors being returned from the Gmail API, see the Gmail API reference.
You can also check the status of the Gmail API for any possible service outages.
Having difficulties connecting to your Gmail account? Try reauthorizing your account in Settings –> Accounts, or deleting the account and adding it again.
You can find a list of all your available accounts under Settings –> Accounts.
We are constantly aggregating more data about errors, so if this article doesn’t help solve your problem, check back soon.