This was a pretty popular request. Make sure to check out the new Microsoft Dynamics GP 2016 – Project Accounting fields on Requisition Entry
Microsoft Dynamics GP 2016 – Project Accounting fields on Requisition Entry – Microsoft Dynamics GP Community
Sales, Purchasing & InventoryMicrosoft & the GP EcosystemGP 2016
Archived post from 2016. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.