Monetizr charges transaction fee from all transactions that go through it's API or plugins.
Monetizr charges fee on every purchase made through the platform. Amount of fee depends on subscription tier which you can find here.
For smaller studios Monetizr offers free tier with higher fee on all sales. All costs a are paid by player and not the studio. It allows developer to implement Monetizr for free.
For medium to enterprise level customers Monetizr offers to