I have premium on the shop and I'm level 3 but when I do one las purchase to reach level 4 I get an error that says "an exception has occurred" and it doesn't let me continue playing

Yep it's a bug, i'm sorry about that, use "rollback" on the bug screen (on bottom)
Then don't buy token again, for now, it will be fix on the 0.2 in few day.