For the correct registration of Freight costs based on the Carrier Selection some default Business Central settings must be considered

After correct setup the Service Charge Account will be inserted in the sales order as a default and when Carrier Selection is functional the selected services will be calculated.

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Note: If you work with the carrier selection function and your package dimensions are manually changed in the sales order package line the changes will only be copied to the transportorder when the ShipIT Setup Base transport order on is set to Unposted documents

Adding Service Charges is standard Microsoft Dynamics 365 Business Central functionality enhanced by ShipIT.

See https://learn.microsoft.com/en-us/dynamics365/business-central/across-prices-and-discounts?tabs=current-experience#work-with-invoice-discounts-and-service-charges.