So it would seem that the issue is with ERP application returning the information.
This probably hinges on what you are defining as returning?
In your function description you note that the function issues documents.
Is that what you are using to determine that the function has completed?
The function makes some calculations, then INSERTs and UPDATEs data (the aforementioned documents) then returns 1 row with 3 columns with information on whether there were any errors or how many documents were created and so on.