Also, to be clear, QURI didn't end up using this system to distribute prizes.
FYI, the lottery system described above as a means to distributing prizes is illegal in the US (states have a monopoly on random lotteries, unfortunately)
Basically, if a payment system involves three features together, it will likely be illegal:
The typical way around this is to get rid of consideration and give an alternative means of entry, e.g. “you can also enter by emailing this email” or similar. This is why promotions often have the “no purchase necessary” language in the US. There are ways around this, but typically you need to apply for a license.
[Credits to Abraham Rowe for catching this.]
Location: London, UK
Willing to relocate: Yes
Involvement with EA:
Drop me a message if anything above sounds potentially useful; I will be glad to hear from you :)