I paid and no download happened - how can I fix this? I followed the basic capture routine of Open OS that you can't download without a Credit Card.
You are of course not required to pay. If you did the devs will surely appreciate it though.
Your question gives almost no details on what problem you are facing. If you did not see the window with the links to download the torrent files, you can just go to https://elementary.io, enter $0 and click the "Download" button.