Thak you for your reply @yabapmatt.
For now I will do more research on your project which I really love. I want to try to make some applications for steemmonsters and I was interested in understanding the dynamics of the exchange of cards between users, to see if it was possible to use the scrow in these cases. But this is going to take a lot of time because our programming skills are quite limited.
By the way, for your information, luckily I own steemmonster.net.