I have no problem paying €4 or even €40. Problem is that I don't know when I can be locked out of an app due to Apple or Google policies. Not the fault of the creator(s), obviously.

That, and as another commenter pointed out: network effects. I'll pay alright, no worries. But how I even test the thing if none of my people are there?

And why no free trial? I'd evaluate the messenger in maximum 30 minutes.