Firstly find where your people are. If they’re on a certain platform, go there. This is all about research, don’t just canvas every group, every platform, every page with the same promotion because that is just spam.
Next, you need to specifically tell people why they should use it, don’t give them the full tech spec because whilst a handful of people may like reading it the majority will see more than a few words and think “I can’t be bothered to read that” and move on. Your promotion needs to show that it fixes a problem or offers something unique so make sure your content actually does that.
Interaction is key, you’ve found your audience, your content clearly says “hey, you have this problem, this app fixes it” but people will have questions, even when it’s stupidly obvious people will have questions. “Where do I sign up? Does this work on XYZ device? Does it cost?” Etc. maybe come up with a list of Frequently asked questions people ask you and give decent but short answers, the trick here is to make sure to actually answer the question but don’t give them huge ass essays.
That is pure organic growth. It takes a while but in my experience I’ve found organic growth where you build relationships with people have a higher retaining rate than throwing bots at everything, hammering things with ads etc, obviously those are options as well but by doing steps 1 and 2 you could then use those to run ads and what not across your platforms :)