8 months gone since launch and I reached 7k active users of Learn Azure mobile app. 6 or 8 months of this period I am mostly did not touch advertising or doing promotion.
Below, I summarize what was working in my niche of preparing for certification exams in IT:
First post in private Facebook group that specialized in preparation for exams on Azure. That was to bring about 500 downloads in 2 days
Posts in all Facebook groups about Azure. Not all of them passed the promotion, but in most cases post passed the moderation
Google Ads! Last 2 months I spent about $300/mo in paid advertising. Before that I hired a marketer which created promotion designs and setup ad. Cost per install starts at 8¢ for Asian Google Play markets and about 1$ for USA/UK/Australia and West Europe.
I am keep going.
App to check (and probably left feedback ;):
https://play.google.com/store/apps/details?id=com.learnazure.app