Purchase order (PO): why a hospital or county may refuse to pay a ride invoice that lacks one

What is a purchase order, and how is it different from an invoice?

A purchase order is the buyer’s numbered approval to spend money on your service, issued before the ride. Four other documents often sit beside it:

• Contract or master services agreement. The terms that govern the work. The master services agreement entry lists them.
• Rate sheet. The prices and nothing else.
• Invoice. Your bill. It cites the purchase order it is billed against.
• Trip authorization number. The ID a Medicaid broker or state assigns to one approved ride. Read the trip authorization number entry for how it works on a claim.

The PO does not set your price or your duties. It tells the buyer’s payment system that a purchase was approved, for how much and for what period. Federal agencies issue purchase orders too and also use blanket purchase agreements, covered in the BPA entry. The facility billing guide covers the rest of a facility invoice.

Why do hospitals and counties want the number on the invoice?

They use the number to tie each invoice to an approved order. Mass General Brigham is a clear example. Its orders must come with a PO in its format, a number that starts with PO- and has eight digits. Its invoices must show the invoice number, the invoice date, the PO number and the remit address, with only one PO per invoice. A mailed invoice carries the PO number on each page, and the hospital does not accept statements, agreements or spreadsheets in place of an invoice. Its suppliers are told that an invoice that does not follow the procedure may be paid late. The hospital vendor guide shows how that fits into becoming an approved vendor.

Public buyers have their own versions:

• Maryland. Under section 15-102 of its State Finance and Procurement Article, an invoice on a state procurement contract must include the contractor’s tax number, the contract or PO number or another adequate description of the contract, and any documentation the contract requires.
• Federal agencies. A proper invoice under 5 CFR 1315.9 includes the vendor’s name, the invoice date and number, the government contract number or other authorization for the services, a description with price and quantity, and the tax ID.
• Texas. The late payment interest rules for governmental entities do not apply when an invoice is not mailed in strict accordance with any instruction on the purchase order about payment (Government Code 2251.002).

What does a blanket purchase order look like for recurring rides?

One approval can cover a period of rides instead of one ride. Stark County, Ohio, shows the pattern in its public minutes. At its December 17, 2025 meeting the commissioners approved five Job and Family Services requisitions labeled NET Transportation Contract. Each line names a vendor, the contract dates July 1, 2025 to June 30, 2028 and a dollar amount, from $600,000 to $1,600,000. The same meeting approved a change order that raised one vendor’s earlier amount from $420,000 to $520,000.

For dialysis or standing discharge work, a facility may set up the same way: one number, one amount, one period. Ask which it is, since the invoice has to match it.

How does a purchase order run out?

It ends when the amount is used up or the period ends, whichever comes first. A change order, as in Stark County, is how a buyer adds money. Here is an example. A $50,000 order with $4,200 of rides invoiced each week covers about 12 weeks of work. A ride company that invoices on week 13 has no money left under that order.

Keep a running balance for each PO: the amount, the invoices billed against it, and what remains. Ask for an increase when about a fifth of it is left, since an approval takes time.

What if the facility says there is no PO?

Ask what reference the buyer’s payment system wants, and put that number where a PO number would go. Some buyers pay from a contract or an authorization number. Maryland accepts another adequate description, and a federal invoice may carry another authorization. Others, such as Mass General Brigham, require the PO itself.

Before the first ride, get the approval in writing, with who approved it, the amount and the dates it covers. A verbal go-ahead leaves the accounts payable clerk with nothing to match your invoice against.

Putting the PO number on the invoice

Print the number in the same place on every invoice, next to the invoice number, the date and the remit address, and follow the buyer’s own format. Mass General Brigham, for one, takes emailed invoices only as an unencrypted PDF or TIF that holds nothing but the invoice. The invoice template has a box for the number.