https://www.tryaqueduct.com/
It has a concept of percentage-based billing where you can specify an input amount and you can specify to bill a percentage of that and handles generating a detailed invoice.
It has a concept of percentage-based billing where you can specify an input amount and you can specify to bill a percentage of that and handles generating a detailed invoice.
Whenever there's no pricing it immediately says "not for me, move on". Maybe that's your intention!