Small suppliers selling to larger organizations frequently find that the sale closes quickly and the payment does not. The purchase order process explains most of that delay.
The order is the buyer's control point
A purchase order commits budget internally before money leaves. It records what was authorized, at what price, against which cost center and under whose approval.
Accounts payable in a controlled environment will not pay an invoice that lacks a matching order. The invoice is checked against the order and against the receipt of goods.
That three-way match is the reason a perfectly valid invoice can sit unpaid indefinitely: one of the three documents is missing or disagrees with the others.
Work started before the order is at risk
A supplier that begins delivery on a verbal instruction has no authorized commitment behind it. If the requester leaves or the budget is reallocated, there may be nothing to invoice against.
Retrospective orders can usually be raised, but they require someone inside the buyer to justify an unauthorized commitment, which they have little incentive to do quickly.
The practical rule is that the order number, not the buyer's enthusiasm, marks the point at which work is safe to begin.
Vendor setup is a separate queue
Before any order can be raised, the supplier must exist in the buyer's system, with banking details, tax documentation, insurance certificates and sometimes diversity or compliance attestations.
This process runs through departments that have no interest in the transaction and no deadline attached to it. Weeks are ordinary.
Starting vendor setup during the sales process rather than after it removes a delay that otherwise lands entirely after the commitment is made.
Small mismatches stop payment silently
An invoice quoting the wrong order number, a different description, a quantity that does not match the receipt, or a total that includes unlisted freight will be held rather than queried.
Nobody tells the supplier. The exception sits in a queue until the supplier chases, which is why disciplined follow-up on aged invoices matters more than the payment terms themselves.
Matching the invoice line-for-line to the order removes most of these exceptions and is entirely within the supplier's control.
Terms and cash flow are separate problems
Stated payment terms describe the period after a correct invoice is accepted. Time lost to setup, order issuance and exception handling sits outside that clock.
For a small supplier, the gap between delivery and payment must be funded from working capital, and a large order can strain cash more than a small one improves profit.
Federal and state prompt payment rules apply to some public contracts and vary in scope, so a supplier dealing with government buyers should confirm which rules apply to that agreement.