QuickBooks Desktop sync error: There has been an internal error when processing the request
Why the sync error occurs
This error occurs for various reasons and is related to updates made to vendors or accounts.
How to fix the sync error
Vendor integrated bill pay or payroll service
QuickBooks does not allow another application to update the "locked" vendor record. Manually make updates to the vendor in QuickBooks.
Contact Customer Support to clear the sync error.
Payment was recorded manually
Delete the manually recorded payment from QuickBooks, which will allow the payment record from Bill.com to sync to QuickBooks in a subsequent sync. If the payment can't be deleted from QuickBooks manually, contact Customer Support to request that the payment be marked not to sync.
Bill no longer exists in QuickBooks
Contact Customer Support to request the record updated in Bill.com be marked not to sync. After the record is marked not to sync, record a manual update in QuickBooks.