It only works once per wallet, but you can use it with differents wallets and... it gives you between
5 and 10 Ksat. (depending on what you do to promote their web, 5 if you don't do anything, 2 more if
you tweet 2 if you post on face... and so on...)
It gives you a temporal wallet, but it's not important, you don't need to take a note of it or anything, at the end it will ask for your real wallet to pay you.
