You won the contract. That part is done. Getting paid on time is a separate skill, and it is not one anyone teaches you before your first award.
The government does not accept invoices the way a normal client does. There is no emailing a PDF to accounts payable. Which system you use, how you format the invoice, and when the clock on payment actually starts are all set by regulation, not by you.
Find out which system you are required to use
Most Department of Defense contracts require you to submit invoices electronically through Wide Area Workflow (WAWF), now part of the Procurement Integrated Enterprise Environment (PIEE). This has been mandatory since 2008, when DoD amended the DFARS to make WAWF the only acceptable way to submit invoices and receiving reports on DoD contracts (DFARS 252.232-7006). You register once at wawf.eb.mil, tied to your SAM.gov entity record, and every invoice on every DoD contract runs through it after that.
Civilian agencies more often route through the Invoice Processing Platform (IPP), a free, web-based system run by Treasury's Bureau of the Fiscal Service. IPP lets you upload invoices against a purchase order the agency already loaded, track approval status, and get notified when payment clears.
Check your contract's payment instructions clause before you invoice the first time. It names the system. Guessing wrong wastes a cycle.
Know what a "proper invoice" actually requires
The Prompt Payment Act clock does not start when you submit something. It starts when the billing office receives a proper invoice, meaning it has everything the contract's invoicing clause requires: contract number, invoice number and date, description and pricing of what was delivered, and the correct billing office address, among other required items (FAR 52.232-25). If the invoice is missing something, the billing office is supposed to reject it back to you within seven days. That rejection resets your clock, not theirs.
This is where most delays actually happen. Not government slowness. An invoice that does not match the contract's stated format.
Understand the actual payment timeline
The Prompt Payment Act sets the government's payment due date as the later of two dates: 30 days after the billing office receives a proper invoice, or 30 days after the government accepts the goods or services (FAR Subpart 32.9). Whichever comes later governs. If your invoice sits waiting on acceptance, the 30 days does not start until acceptance happens.
If the government misses that due date, it owes you an automatic interest penalty, without you having to ask or file anything, as long as the invoice was proper and the delay was on their end (Treasury Prompt Payment FAQs). That penalty is set and published, not something you negotiate.
None of this guarantees fast payment. It sets the rule the government is bound by if the invoice is correct and the work is accepted. Getting there is still on you.
What actually slows contractors down
The same three things, every time. Invoicing before the receiving report shows the government accepted the work, so the clock never starts on your end. Line-item pricing that does not match the contract's schedule exactly. And a billing office address pulled from the wrong section of the contract. Each one is a rejection, and a rejection is a new seven-day review before the clock even begins.
Building past performance and winning the next contract both depend on this cycle running clean. Late payment does not just cost you cash flow. It is the kind of friction a contracting officer remembers when the recompete comes around.
If you are still building the pipeline that gets you to an award in the first place, our features page covers how we track a bid from opportunity to signature, so invoicing is the next problem you have, not the first one you are guessing at.
WAWF and IPP are the actual systems your invoice routes through once the receiving report clears, and how progress payments change the math on larger contracts is worth reading before your first delivery, not after a payment goes missing.
Related reading
- How to Write a Government Contract Proposal (Section-by-Section)
- Past Performance: How to Bid Competitively With None