Ehh, I don't know if that counts. Lots of sites want me to join on my phone or download an app, even though they are desktop compatible.

I'm irked when companies go for this form of anti-documentation. It 1) makes me feel dumb 2) wastes my time 3) I'll eventually figure out what you're not telling me, so you might as well cut to the chase.

It seems "Join on your phone at paperplanes.world" actually means 'Join on your phone with Chrome browser at paterplanes.world'

Firefox is my primary browser even on Android. It didn't work on it, so I suspected and tried it on Chrome. It works there.