This error message appears in the Sync details panel when a supplier sync cannot run because another sync is already in progress for the same integration. The supplier is not synced on this attempt, and the Suppliers row shows Failed.
Cause
A supplier sync (manual or the scheduled nightly run) is already running for this ERP integration, so an overlapping sync cannot start.
Solution
Wait for the current sync to finish - on the Overview tab, the row shows a loading indicator and the Sync now button is disabled while a sync is running.
Once it completes, run the sync again.
If the status stays Failed after the running sync has finished, contact Payhawk Support.