One problem is that your game is not provably fair. The owner could pretend both players lost and bank the money, so unless you build a provably fair implementation into it the owner will have to demonstrate their trustworthiness in order to attract players.
Also I would recommend you build it as a mobile friendly web app instead, as few people will be willing to install a game like this. An advantage of that is that people could still play from a computer or non-android phone. Also you are already building the server-side stuff in PHP, so why not the client too, it will avoid some complexity.
Hi greyhawk,
Thanks for the help, I think someone also asked about this above.
Before the game starts, we'll show some hash values, with a hashed salt, on a display, which would prove the position of the coin in each box, for each round. and then release the unhashed salt, to prove it equals to its hashed value ...
For this project, I'm aiming at developing an interesting, fun, pvp game, which is absolutely transparent. So any other way/suggestion to make this happen would be absolutely great!