Did I mention that as reward cards, we get them for playing the game :-)
It is worth to mention the fact that nowadays much more rarely than in the past. You can complete many daily quests without receiving any reward cards. But there is an upcoming change in the reward system from the developers. Hopefully the reward cards will be more frequent than now.
Good luck and have fun.
Have a nice day. All the best. Greetings and much love from Hungary.