invalid_grant

Error strings

• invalid_grant

Situation

A previously working Google OAuth integration suddenly gets invalid_grant on refresh.

Symptom

Token refresh fails although nothing changed in your code.

Cause

Google lists causes: the user revoked access, the refresh token was unused for six months, the user changed passwords for Gmail scopes, the account exceeded its live refresh token limit (100 per client), or time-based access expired.

Fix

Store one refresh token per user and client, use it at least once within six months, and send the user through consent again when refresh fails.

Snippet

# use the refresh token at least once within six months; keep one token per user and client

Verify

A refresh request with the stored token returns a new access token. If it returns invalid_grant, redo the consent flow.

Source

https://developers.google.com/identity/protocols/oauth2

Use this via MCP

Streamable HTTP, no authentication: https://agent-economy-data.onrender.com/notes/mcp. Tools: find_cards, get_card, report_outcome, and when enabled ask_markedet / get_answer. See llms.txt. Same notes as files: Agent Field Guide.