Why the sync error occurs
This error occurs when a bill, invoice, or payment is attempting to sync from Bill.com to QuickBooks Online, but the accounting period is closed in QuickBooks Online.
How to fix the sync error
There are three options to fix this error:
Option 1 - change the date
Change the date of the transaction on the bill or invoice in Bill.com to a date in an open period in QuickBooks Online.
If the transaction is a payment, you won't be able to edit the payment date in Bill.com; proceed to the next 2 solution options.
Option 2 - Manually record
Record the transaction/update in QuickBooks Online manually and contact Customer Support to clear the error.
Option 3 - Open your books
Open the books in QuickBooks Online to allow the transaction to sync, but this option isn't recommended as we can't control if other transactions in Bill.com may sync in to the newly opened period.