Slack OAuth refresh token invalid_grant — What it means & how to fix it

OAuth token refresh issues can disrupt integrations with Slack, particularly when the error "invalid_grant" indicates that a token has expired or been revoked. This scenario typically arises during token rotation, a feature Slack offers to enhance security but which also introduces specific failure modes. Token rotation must be enabled to receive refresh tokens, and developers must ensure they use the most recent refresh token, as each successful refresh invalidates the previous one. Access tokens are short-lived, necessitating timely refreshes before expiration to avoid invalidation. Additionally, mismatches in client credentials or app uninstallation can result in token invalidation. To prevent these issues, engineers should enable token rotation, store the latest refresh token, refresh tokens before they expire, and establish a re-authentication flow for users. Tools like Nango offer solutions to manage OAuth token lifecycles effectively, automating refresh processes and handling concurrency safely.