Our app costs $18 per month and one of our customers said she could buy only using a PO. So, I told her to use it for free till she finds a way to pay by card. We are likely to gain more by having an enthusiastic user, rather than losing her for the stupid purchasing department.
So sell her an enterprise subscription for $2500/year, with up to 10 logins, and take the PO. Now you have a year to figure out how to make that routine.
We have 800+ small businesses as customers. This one is from a large company who don't come in as inbound lead. Don't you think it is better to understand how to work with them rather than hitting a wall with their purchasing department?