Please log into the admin portal at admin.xogo.io (enter the same username/pass that you use for the XOGO Manager app). You should see in the account > billing section that you have a credit for X number of dollars. You can use that credit to "buy licenses" for your account and then you can add your players to XOGO Manager.
Here's a little video from showing how that is done: https://www.youtube.com/watch?v=LsJhgZSoc4U
What is the reason for this extra step? It's actually to save you money! Each software license that you purchase from XOGO allows you to run one player for X number of months (usually 12 or 36). When you purchase a license in the XOGO Manager app the clock starts ticking immediately. But when you purchase via a PO, we actually credit your XOGO account for X number of dollars and the clock doesn't start ticking until you go into the admin panel and turn that credit into software licenses. That way our large customers in particular don't lose 1-2 months of license time while they are deploying their players around the country/world.