Hey, thanks for checking out the post!
If you participate in the related community game jam and win it's paid: https://itch.io/jam/bankshot-community-jam
Otherwise we can't offer anything unless we really like the levels you are making and we'd commission you to make more for us :D
Builder is currently open for everyone and accessible through Community in-game https://maciaz.itch.io/bankshot
Remember though if you'll want to publish the level, you have to login with your itch account, it's right at the Start screen