Hi Ivy,
Thanks for the response. I was aware of most of what you said and my main concern was if the supplier submit an invoice to AP and also creates one in SUS, the system won't stop them. And we can't expect AP to monitor this when they receive an invoice.
But that BADI looks like it will do the trick. So if we have a GR of 100 units, and the supplier submits a paper invoice for 40, forgets, and then creates a SUS invoice for 100, it will give them an error.
Thanks,
Seth