Contra charging and Purchasing Accruals

 I'm investigating the use of contra charging and would like to know the effect on purchasing, specifically accruals. The scenario is as follows - we plan some marketing activity with our customer so generate a PO for the spend and receive the service. The customer deducts the value from their next payment. I create an invoice in AP and match it to the PO. I don't want to pay the supplier as the money has already been withheld. By using contra charging I can create a credit note in both AP and AR for the customer / supplier. I match the credit