If there is a sales group indicated for the customer, it will be transferred automatically when you create the order.

Click the square arrow in the field to select a different sales group for the current order. When the invoice for the current order is updated, the information about the sales group is saved in the invoice journal and used again for calculating commissions. You will find additional information about how to set up sales groups and commission rates in the dialog boxes in the Commission sales group (form)and the Commission calculation (form).