After you have uploaded your application for payment and it has been approved by the contractor, you will might be required to Submit an invoice against the application to complete the application process and receive payment.
Once you receive your payment notice, login to WebContractor, navigate to the application you wish to Submit Invoice for and choose Submit Invoice option from Actions menu in top right corner:
This will open the following screen, where you will need to fill in the invoice number, upload an invoice document, and tick the checkbox:
When you check all information click Submit Invoice