Hopefully someone with some benchmarks on this specific kind of thing can chime in, but to me it seemed like 8-10% conversion from notification to install was not too terrible. Don’t get me wrong, it sucks that it turned out this way! I’m just basing this on conversion percentages I’ve seen from email launch sequences (maybe 2-5% of the list), webpage conversions (free signup maybe 10,20,50% but paid 1-5%), and 8-10% for a nearly-cold install notification seems kinda in the ballpark.
There’s a correlation I’ve noticed between how easy it is to sign up for a thing, combined with how badly someone wants that thing, and then how likely they are to actually buy/download/etc. In this case it was super easy to click that “pre-subscribe” button so I’d think those people aren’t very invested. There’s only a tiny bit of time for them to form a connection with it, so when that notification pops up hours/days later they might not even remember they clicked that button, or don’t remember the name, etc.
It’s a bummer it was so expensive though! I went through a couple expensive YouTube paid promo experiences recently that took me by surprise too. Just like nowhere near the performance I hoped for. Not fun!