48 CFR § 52.213-2 - Invoices.
As prescribed in 13.302-5(b), insert the following clause:
The Contractor's invoices must be submitted before payment can be made. The Contractor will be paid on the basis of the invoice, which must state (a) the starting and ending dates of the subscription delivery, and (b) either that orders have been placed in effect for the addressees required, or that the orders will be placed in effect upon receipt of payment.
The following state regulations pages link to this page.