I can't install the ios app on my ipad through alstore. I haven't tried any other sideloaders though. I'm using an ipad pro, on ios 15.3.1. Does someone know how to install it?

I have the same problem...

I did find an ipa that works, https://archive.org/details/wheres-20-my-20-perry-3-f

You cannot use sltstore, but sideloadly and trollstore work (I prefer trollstore).