I just purchased StellarMateOS (1.4.2), wrote the image onto a 16G sd card and run the system on a RPi3. Everything looks good so far when using my (Debian-based) laptop -- I can connect to the stellarmate hotspot, I can SSH into the OS, I can access the desktop using VNC and I can conjour the INDI web manager.
Alas, the Android app (beta 1.9.11, Bundel v23) won't find the device, although my phone (Galaxy S9 running LineageOS) successfully connected to the stellarmate hotspot and I successfully logged into my stellarmate account (I think -- does the app give any feedback about login state? Is there any [Log out] button?)