We are currently on monthly billing which is great. But every time we add a new device we have to track down a credit card and separately purchase that many extra licenses, which is a huge hassle.
With most of my other monthly subscriptions we can increase the number of licenses on the fly and the charge just shows up automatically on the next monthly bill.
In monthly we usually use credit added to your account to get a similar result. You can for instance add 500$ and then all the licenses you purchase will be taken from this credit. It will avoid having to make a purchase for each license. Would that answer your needs?
That's certainly not a bad idea. But it's still not quite what we're looking for. We would rather pay for what we use when we use it.
Where we bill our clients monthly for the service, it's easier to pay for it monthly as well. That's even more true as we scale up the number of clients.