[EDIT: Updated to correct explanation of unposted AP payments to posted AP invoices]
Hi Kirk,
You are correct that this has definitely been encountered before by others, but unfortunately the application of AP payments to AP invoices is not supported by either IM or eConnect. Based on how that process currently works in AP, I suspect that it will probably never be supported.
However, with that said, it is technically possible to apply AP payments to invoices with custom code and custom SQL.
But there is a big caveat.
If you are applying the unposted payments to posted invoices, it is only moderately difficult to develop a custom integration. I developed an integration that imported manual payments, and then applied the unposted payments to the open invoices. This took a fair amount of reverse engineering and work, but the solution works well.
However, if you are applying posted payments to posted invoices, then it suddenly becomes a much more complex solution.
The reason for the complexity is that when you apply a posted AP payment to a posted AP invoice, if the invoice is paid in full, it moves it to history immediately and does additional housekeeping, such as update vendor balances. It is similar to bank transaction imports in that there is no batch, and the 'posting' occurs immediately, and there is no "oops" button. This means that there is alot more SQL activity, and quite a bit more complexity.
I have done the research to reverse engineer that process, and although it is probably technically possible, it would much more complex.
Let me know if that helps, and if you have any additional questions.
Thanks,
Steve Endow
Dynamics GP Certified Trainer
Dynamics GP Certified Professional
steveendow@gmail.com