Field help (PAYBAN) 

Use this field to indicate the payment bank associate to the site.
This information is displayed in the default initialization of the bank code in payment invoice entry when this information is mandatory.
The initialization is based on the following order of priority: the customer or supplier bank/cash funds and the bank entered on the site. Then, the user parameter BANKDEF - Bank by default, is used for banks and the user parameter CAISDEF - Default cash (chapter TRS, group DEF) for cash.