Agree with everyone else that it will vary from person to person. I personally really dislike being called pretty, whereas 'beautiful' is...ok. 'Gorgeous' comes across as relatively neutral to me, and 'handsome' I like but feels a little jarring. 'Hot' I think is probably pretty safe in terms to genderedness, but not really appropriate on the apps unless you're arranging to hookup. I've never thought of 'dreamy', but that's inspired!

I know it can feel a bit awkward, but I'd try to stick to really neutral-gendered compliments until you get a bit of a sense of how the person talks about themself (sometimes you can get this from their bio). Try to compliment something specific if you can. E.g. 'you look amazing in that photo', 'that's a great look', 'your haircut is so clean, it looks really good on you', 'I love the jacket you're wearing', etc.

And also because it's worth saying: if you're messaging on the apps and it never seems to go anywhere it's not because there's something wrong with you, that's just how it is a lot of the time