it is $10 on itch.io. Are you sure you have bought the quest version of the game?
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Yes it was $10, I paid an extra 10 because the game is so good. I think I had the full version and didn't know it. I played and won a few rounds and was able to buy more planes and go on more missions. But I ran an update, and it is back to the demo version. I will have to see if I can get it back. The book at the beginning scene said "Demo" right now.