Steve Endow finds that Dynamics GP Web Services does not support importing sales taxes for SOP Sales Orders. I was stumped too because I could swear I’ve done it. GP Web Services supports importing sales tax for SOP INVOICES, but not ORDERS. Ugh.
Dynamics GP Land: Dynamics GP Web Services does not support importing sales taxes for SOP Sales Orders
Development & IntegrationSales, Purchasing & Inventory
Archived post from 2014. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.