Hi, thanks for getting in touch!
The jam generally doesn't have strict requirements, however in the spirit of a game jam format it's generally perferred that games will be made for the jam during the jam period, at most integrating minor/structural parts of an earlier engine/project. This is to encourage people to share their dev experiences, learn/try something new, and put the games on a more equal footing (although the competitive aspect of this jam is relatively light).
Due to vote brigading this jam has a voting system that is open only to other participants - for that reason if the game is limited to those that pay for it, there may not be too many people voting and interacting with it.
I hope that answers your question! Best of luck with the larger project that you're working on.