StarShip can access any user-defined fields you define in SAP B1. You can create user-defined fields in Tools > Customization Tools > User-Defined Fields – Management.
User-defined fields will be available for you to map to StarShip fields (in Setup > Source Interfaces > SAP B1 (version) > Interfaces tab > Customize Interface) so that you can import their values into StarShip shipments. To map user-defined fields in StarShip, select Setup > Source Interfaces > SAP B1 (your version) and click the Interfaces heading. Then, click the Customize Interface button for Sales Orders, Deliveries, or Invoices.
You can also set up write-back of shipment details to Header and Package level user-defined fields when you process a shipment in StarShip. See SAP B1 Custom Write-Back for more information