Coins are harder to obtain, especially after completing the initial achievements. Coins are the only way you can sign weekly Featured Players and the way to go if you want to unlock top Managers early on.
You get 10/10/10/10/10/20/30 coins by logging in to the game from day 1 to day 7 (weekly), and sometimes PES will simply give you coins as a reward for participating in a competition or when a product launch or their celebrations like anniversary, special day etc..
Obtaining coins takes a while, but there is one way to speed up the process - you pay real money for coins. That’s how Konami makes money, after all!