Integration itself shouldn’t be an issue. Many exchanges provide apis. The issues are likely about the exchanging process itself though. Depending on the jurisdiction you’re in, all sorts of regulation could kick in to the point where you might need some license.

It’s all rather ludicrous, imho. If Damus was one of those pay-to-level-up type of games you could simply sell tokens or gold stars through the app store and nobody would bat an eye.