Pokémon Masters has just been released (August 29, 2019) and you will quickly realize that the in-game currency, diamonds, is very important for obtaining powerful Sync Pairs. Diamonds will also allow you to purchase various items in the Game Shop, but its main use remains the summoning of Trainers and their Pokémon. As in all GatchaGame, these are classified with stars (5 stars being the strongest).
Anyway, here’s how to get Diamonds in Pokémon Masters: