In User Security Default Accounts Payables, Vendor Prepayment Accounts have been added. They are the following as follows:
Vendor Prepayment - Bank Account - default Bank Account
Vendor Prepayment Account - default Accounts Payable Account
In Vendor Prepayment form, default A/P Account should be populated in Account field. Default Bank Account should be also populated from the User Security Default Account settings.
Reference: Task 6147