AP invoice mapping for deduction

Summary:

We have here, on external application namely Service Purchasing. What this application do is roughly, collect all the claim from vendor and we as the client will pay what the vendor job is done. In this case, vendor has done one job for client, and claim in one work order. In that work order we have one deduction, this deduction once goes to Fusion App, it doesn't go to the correct account. How to see the AP Payable account mapping for this deduction.