Percentage of earnings

Check out last stream about Marketing for more information.
You pay revenue from money that was generated by your project - does not matter how: sales, ads, in-game purchases and other stuff mentioned in EULA.
Difference between donations and other payments is fundamental. If your game is totally free and any user could play in full version without restrictions without additional payments - then you have clean donations and you’re free from revenue payments. But if donation grants access to some additional stuff in your games then it is a different story and you have to pay royalty.
Check out this part about Kickstarter from EULA

Disclaimer: Could be wrong, check everything by yourself :stuck_out_tongue: