the undersigned further certifies that to its best knowledge and belief, each of its supply of services has made full payment of all costs, charges, and expenses incurred by them or on their behalf for work, labor, services, materials and equipment supplied to the foregoing premises and/or used by them in connection with the undersigned's work under said general service contract for the above referenced scope of supply, or certifies that the receipts from the payments made against the invoice that accompanies this certification will be used to make such full payments.