Ah, that’s a trick question! All customers must provide payment to 99designs before the design contest is launched.
After you’re selected as the winning designer, upload your final design files as soon as possible. Once the files are approved by the client (in the Design Handover stage), we’ll add 99designs credits (also called "earnings") to your account in the amount of the stated prize.
You will receive the automated payout based on the info provided on this page:
https://support.99designs.com/hc/en-us/articles/204108819