Trust Transactions Not Syncing to Quickbooks Online with Sync Error 6140
Quickbooks Error Code (6140): Duplicate Document Number Error
Quickbooks Error Code (6140): This number has already been used. DocNumber=(Number) is assigned to Journal Entry
These resolution steps are specific to manually entered Trust Transactions unrelated to payments against Bills or Trust Requests.
A specific setting was enabled in Quickbooks Online resulting in Trust Transaction sync error (6140): Duplicate Document Number Error.
It could also be caused if a Manual Journal entry was made in Quickbooks and now Syngency is trying to make a new Journal entry with that same number
In Quickbooks Online:
Select Advanced Settings
Disable “Warn if duplicate journal number is used”
Select Bill Syncing
Locate the Error Code by scrolling down
Wait for the next sync cycle to re-sync.
If the steps above don't work, the manual journal entry may have to be deleted.