Usually paid in advance, often acts as a barrier, and always a signal – how to price your work is a tricky subject for many freelancers.
Price to build a reputation, to do it again, or never have to do it again. Free, and it could be for anyone. Expensive, and your name might not be on the list.
You could define enough and in defining enough, be secure enough to defer your payment until you demonstrate that you can create enough value for everyone.