3 Way Matching workflow cannot find matching PO for the vendor bill.

Hello everyone,

I have a slightly customized 3 way matching workflow (only customization is the visibility of the buttons to certain roles). Now when I create a PO, an item receipt and a bill, normally the workflow should approve that bill automatically because the quantity and amount are equal and there is no difference tolerance used. However, the workflow always goes to 'pending approval' state which requires manual approval. In the second state 'Bill validation' it creates and exception saying ' No matching PO can be found for the Vendor Bill' and thus sees the bill as standalone. Any idea why this might