Yes, it is a revenue.
It's not "FEE FREE", so you have to pay the fee.

It is "FREE FEE", which means they don't charge you for paying the fee.

But, you'd be surprised how more and more US companies are charging you an extra fee if you make payment through any method except direct debit from your checking account online. It wasn't long ago when you could just pick up the phone and pay a bill, either through a live person or through an automated system, and there would not be any additional charge to pay your bill. That's not the case with many companies now. And, they don't always tell you; sometimes it's buried in the fine print. It's amazing how more and more companies employ more and more tactics used by scam artists and con men.