Hi, sorry I may not have fully understood the question.
That is to say, it often happens that the amount payable is greater than the Purchase Invoice amount posted in the system? I don't think this can be done in the system and it looks like a company process issue.
If you need the amount to be consistent with Purchase Invoice, it is recommended to use Credit Memo to cancel the original posting and create a new invoice. But this also generates new numbers.....
I hope other experts can give you better advice.
Thanks.
ZHU