1.: When complete a Level with the Win conditions in Challenge or Quickplay mode you get a lot of Ressources!

2.: You get them as soon as you finish the last Hand. Do NOT click on "Claim Reward"!

3.: Restart the Last Hand in a Level will give you Ressources and you can just do that one Hand over and over again to get as much Ressources from the Level finish reward as you want.

The Restart will cost you 1000 pure. But Most of the time you will end up with a positive outcome, because the "pure this hand" still counts too.

Best to do in first Level or if you need a Perfect in a challenge in the last level (thats how i found it)

Here are 2 Screenshots.
Before:

And after a few Hands: