ERR_ZOHO_SYNC_FAIL on Zoho CRM: Zoho CRM sync failed — records are not being created or updated, or the integration reports a failed batch after a Zoho CRM API response. Root cause: Zoho CRM synchronisations usually fail at one of four points: the connected Zoho OAuth refresh token has been revoked, a required field or layout rule rejects the payload, the integration is using the wrong module API name or record owner, or a bulk import exceeds Zoho’s API and concurrency limits. A generic sync failure is therefore only the wrapper error. The useful diagnostic is the per-record response in the integration run or Zoho CRM API log, which identifies the failed module, field, and error code. Step 1: Capture the per-record Zoho response before retrying. Open the failed run in your connector and expand the Zoho CRM step. Record the HTTP status and Zoho error code for one rejected record. INVALID_DATA points to a field or layout rule, AUTHENTICATION_FAILURE points to the connection, NO_PERMISSION points to the integration user, and TOO_MANY_REQUESTS points to pacing. Do not retry a whole batch until you know which class of failure you have; a repeated bulk retry can create duplicate records when only part of the batch succeeded. Step 2: Reconnect the exact Zoho service account used by the integration. In Zoho CRM, open Setup → Developer Space → APIs and verify that the connected user is active and still has access to the target organisation. Then reconnect the account from the integration’s connection settings. Use a dedicated integration user rather than a personal administrator account, because a password reset, MFA policy, profile change, or user deactivation can invalidate a personal OAuth refresh token without changing your scenario. Step 3: Verify the module API name and required layout fields. Go to Setup → Customization → Modules and Fields, open the target module, and inspect the API Name shown for the module and each mapped field. A label such as Company Name can have a different API name, especially on custom modules. Then open the active layout and list every field marked Required, including fields made mandatory by a layout rule. Send a controlled test record containing those values; an API payload can be valid JSON and still be rejected by CRM validation. Step 4: Check ownership, lookup, and picklist values against the target organisation. For every Owner, Account, Contact, or custom lookup field in the payload, confirm that the referenced Zoho record ID exists in this organisation and is visible to the integration user. For picklists, send the exact configured option value rather than the display text from another CRM. Sandbox record IDs, deleted users, and renamed picklist choices are common reasons a sync works in testing but fails in production. Step 5: Throttle the batch and use Modified Time for incremental syncs. If the response shows a rate-limit or concurrency error, reduce the batch size and add a paced queue in the source integration. For recurring synchronisations, use the record Modified Time as the incremental cursor and store the last successful timestamp in UTC. Add a small overlap window, then deduplicate by Zoho record ID or an external ID field. This prevents missed updates without resending every historical record on each run. Step 6: Replay only the rejected records and verify in Zoho CRM. After correcting the mapping or connection, replay a small sample of the failed records first. Open each record in Zoho CRM and confirm the expected fields, owner, and linked records were saved. Finally, compare the source count, accepted count, and rejected count in the integration log. Keep the rejected-record export until the next successful scheduled run so you have an audit trail if a stakeholder reports a missing update.