Invoices for services should be compared with the work request and confirmed with a completion report.

Invoices for payments on contracts should be compared with progress payment statements, and completion reports.  Contractual terms should be verified, and the due date should be confirmed in accordance with the payment schedule indicated in the contract.

Accounting should be responsible for coding invoices to the appropriate general ledger accounts.  The account may be indicated on the purchase order or work request, but it should be verified before booking the invoice. 

Once it is properly verified, booked and scheduled for payment, the original invoice should be filed together with a copy of the purchase order, receiving report, work request, progress payment statement, or any other supporting documentation.  After payment, the invoice should be stamped or otherwise indicated as paid.

The accounting system should include an accounts payable, or vendor subledger, to keep track of the balance with each individual vendor.  This subledger should always agree with the control account on the general ledger and should be reconciled at least monthly.