There are several ways to earn coins:
1) You earn coins every 2-3 levels when you're leveling up.
2) You can play Proroom and Invisible room in One on One mode to make coins by winning.
3) You can share a game with your friends and get in-game rewards. Make sure they activate your personal promo code. Press the Share button in the Main Lobby of the game and send an invite via one of the messengers. After your friend reaches the fifth level you will receive 5 coins and 5000 chips.
4) You can get the coins with daily free spin in Belmoslot.
In order to use the Belmoslot machine you need to press "Mini Games" button in the Main Lobby. This machine has 100% win rate, however you don't know which prize you'll get. It's all about luck! And by the way: you can roll Belmoslot for free once a day.