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

Integrating Zendesk with OAuth 2.0 can lead to refresh token failures, often manifesting as "invalid_grant" errors, which disrupt ticket syncs and background jobs. These failures typically arise from token lifecycle issues, such as using outdated refresh tokens due to improper token rotation handling, concurrency problems, token expiration, or mismatches in client credentials and subdomains. To address these issues, it's crucial to persistently store the latest refresh token, ensure atomic token persistence, prevent concurrent refresh requests, and handle invalid or expired tokens by re-authorizing users. Using tools like Nango can automate and simplify OAuth token management by providing built-in error handling, automatic refreshing, and webhooks for revoked tokens, allowing developers to focus more on product features rather than token lifecycle management.