Is it a bug or what because I can't buy upgrades except for the first time. I saw many people said your game was fun so maybe it was my problem?
Viewing post in The Miner Scale jam comments
It's most likely that you didn't have the required resources. The first two special scales that drop (from the water and air dragon) look very similar. We planned to re-arrange the order of the dragons, because we kept getting confused too, but ran out of time.
But if you think you found a different issue, let me know and I will see if I can figure out what's going on!