How would I pay the 5% revenue if my games are free?

Not all of my games are going to be free, but for the ones that are free, how do I pay the 5%?

No royalty is owed on games that earn no revenue. Note that revenue includes advertising revenue or other kinds of free-to-play revenue.

The games in question were the ones completely free which don’t even contain microtransactions. Thanks for your answer.