An integration that previously accessed Gmail can lose authorization without the mailbox being broken. Distinguish an expired access token from a refresh token that can no longer obtain a replacement, and keep the original error before attempting recovery.
Check the failed stage
If a short-lived access token expired, the application should use its supported refresh flow. If that refresh request itself fails, repeatedly calling the Gmail method with the old token will not repair authorization.
Compare the stored credential’s OAuth client and account with the intended integration. A token copied from another project or development environment can have a different lifecycle from the production credential.
Review documented revocation and expiry causes
Google’s OAuth guidance lists causes including user revocation, prolonged non-use, password changes involving Gmail-scoped tokens, time-based grants, administrator restrictions, and token-count limits. A testing-mode OAuth consent configuration can also issue refresh tokens with a short lifetime for Gmail access.
Do not interpret every invalid-grant response as proof of an attack or a demand to reset the user’s password. Review the app’s current publishing and consent configuration and the user’s connection settings through authorized channels.
Restore consent without losing control of the credential
If new authorization is legitimately required, use the application’s normal Google consent flow. Store the replacement securely and retire the obsolete credential according to your operational process. Do not ask the user to send a refresh token or password in a support message.
Retest a narrow, harmless operation and verify which account it uses. Preserve useful sanitized error evidence and record when authorization was restored. If the application was already sending mail when access failed, reconcile uncertain sends separately; a successful new token does not establish that earlier attempts had no effect.
Browse Gmail & Google Account help
References
- Using OAuth 2.0 to Access Google APIs | Authorization | Google for Developers
- Resolve errors | Gmail | Google for Developers
Reviewed against the linked official product guidance on November 3, 2026. Features, limits, screen labels, and access can vary by account, platform, region, and organization policy.