Board Thread:Questions and Answers/@comment-68.226.81.85-20150119210446/@comment-68.226.81.85-20150120033301

OP here.

I decided to finally update my iOS system (from 6.1.2 to 8.1.2), and apparently it fixed the purchase error. I was able to purchase the crystals just fine.

Interestingly enough, it also fixed the crashing issue I had for ages and I can run the game with best graphics just fine now.

So if anyone is having problems with purchasing crystals or the crashing, try updating your iOS system.