Every supplier you wish to pay using the Auto banking method must have a bank account number loaded in their Supplier Details window.
Go to Main menu > Suppliers module > Suppliers menu > Supplier Details > select supplier.
From the Supplier Details window, in the Payment Details section, select Direct Credit.
In the Bank Account field, enter the supplier's bank account number.
The number should be 16 digits unless using Westpac which has 18 digits. There should be no spaces between the digits. Tab to move between the fields. Enter any particulars, codes or references you want to appear on the Supplier's statement.