Suggestions:
In Purchase Contract there are is a field as Acceptance criteria. We have to select acceptance criteria from drop down.
It has the option like 1. pay on approval, payment to be done on approval of order. 2. pay on external approval: payment to be done on external approval. 3. can be paid on needful: payment can be done whenever needed.
If users select the pay on approval then, the value of Pay On Approval field in Purchase receipt is selected as Yes, hence a payable Purchase voucher must be auto-generated if the material is fully approved in the QC Order.