We are trying to rebuild a current integration that was done by a prior partner. The current integration creates a customer order, and preposts it with code parts D, E, F. Code part D is the Project, which downstream ensures that the Project is present on the AR Trade posting of customer invoices. In our new integration, we can successfully prepost code parts E and F, but when trying to prepost D, we get an error that an external project must have an activity sequence, which is a field we cannot enter into header preposting. How can I get the project preposting on the customer order header?
Current Integration:

New Integration attempt:
