exactly from which date , linking a vendor for a Accounts payable transaction became mandatory?

Linking a vendor to an Accounts Payable (A/P) transaction has always been built into the strict core database rules of QuickBooks Online and QuickBooks Desktop. There is no specific historical enforcement date because QuickBooks has never allowed a user to save a transaction hitting the Accounts Payable ledger without a Vendor assigned.

If you try to manually map a line item to the Accounts Payable account via a General Journal Entry, both systems will immediately throw a hard stop error message stating: "When you use Accounts Payable, you must choose a vendor in the name field."

Because a transaction without a vendor is systematically blocked, your mismatch is being caused by other common accounting anomalies rather than "vendor-less" transactions.

If you have any additional concerns, please reach out to us again. We’re always here to help.