For the correct registration of Freight cost based on the carrier selection some default business central settings must be considered
Add the Invoice discount to the customer and setup the service charges.
Setting up the G/L posting account for Service Charge
Auto insert function of the Invoice discount. Setup in Sales & Receivables
Setting up the Cust. Invoice Discounts with Service Charge.
After correct setup the g/l account will be inserted in the sales order as a default and when carrier selection is functional the selected services will be calculated.