The first step to earn diamonds is to select a game and click on install, you’ll be redirected to the Google Play Store, once installed start playing and you’ll start receiving notifications mentioning the XP (Game experience) you earn, once you level up you’ll win diamonds.
You can also earn trophies and complete specific missions to earn more diamonds.
In the shop, you can exchange your diamonds against reward cards such as Amazon, Google Play gift cards, Visa Prepaid cards, etc.
Tip: Playing boosted games may help you earn rewards faster. The higher the multiplier, the more diamonds and trophies you'll earn when leveling up the game.