Why the sync error occurs

This error occurs when QuickBooks preferences are set to prevent the invoice number of the bill or reference number of an offline payment to be reused if it has already been used for the same vendor.

How to fix the sync error

If the error is for a bill:

1. Locate the bill
2. Select Edit
3. Update the invoice number to something not yet used by the vendor

If the error is for an offline payment:

1. Locate the payment
2. Select Void payment
3. Record a new offline payment with a different reference number

Alternatively, adjust the QuickBooks preferences to allow for the use of duplicate invoice or payment fields.