This happened to you too.

devid023

I have coins but I can't use them. What's the reason?

Nobody1

This did actually happen to me back when I first started playing; I went several hundred levels before I was able to spend my gold bars. I discovered that once I logged into my Google account on my device, suddenly I was able to spend them. It seemed like it wanted to somehow have access to being able to support purchases, which wasn't possible from its perspective until I logged in. I never want to make any purchases, so my Google account is not linked to any account with money, so I feel safe with it. I don't know that it was specifically my Google account that was involved; I think they just wanted some way to query for money, and until I signed in, there wasn't a way. An Apple account or maybe even Facebook account might fix it too, although I don't know that.

Please note that if you do this, and you want to be able to watch ads for free boosters, you don't want to actually spend any money to make any in-app purchase. If you do, you will probably lose the ability to watch ads for free boosters - they take that away and seem to never give it back once you make a purchase with real money.