Hi there fellow users!
So, basically, I saw this some time ago when trying to make my own app from scratch and I don’t know what to do.But it seems that when you build your app in unity it doesn’t get installed on android 8 but works fine on android 9.I haven’t tried below 8 but I saw that 8 and 8.1 don’t work at all and I don’t know what to do to make them get installed.I have forced the installation to internal storage, it has write permissions enabled and the version company name and stuff I don’t think that matters but I also tried to modify those.I still can’t succeed at making it compatible for android 8 and it might be even below 8 not really sure but I will also try that.I also tried making an empty app and try to install it on an emulated android 8 device via Android Studio and it doesn’t get installed over there neither.It just says could not parse string error.Do you guys have any ideas about what I could do about it? I don’t want to start to work at my project again while knowing it doesn’t work on all devices.
Please share the exact error message, perhaps include a screenshot or two. How are you installing on the device? You’ll want an actual device to test on, not an emulator.
I also tried to install it on some of my friends’ android 8 phones and it just says that the app was not installed.No error message at all.Also, I don’t know if it helps, but one of my friends has an android 9 device like me but he gets a warning that my app is not safe before installing it.
I am installing it using the apk that is created on my desktop when I build it and I just sent it to a couple of people to see if it works all fine, but no luck at all. 
Well, I cannot understand what is really happening.Can I provide something else to maybe help you?As I am not getting any real error messages at all
Does it work in your testing, on your device? Yes, Android typically won’t let an app be installed directly like that without enabling developer options. You could publish your game on Google Play under a test release, then your testers can download the test version from Google Play. But you’ll want to test on your OWN Android device, enabled for developer mode.
I have tested it on my phone already and it works, every time I rebuilt the app I had my phone connected so it imported it in there as well as on my desktop and it works fine.I also have tested further and some devices below android 9 give me an error when I try to install them on the devices.I tested via actual devices on android 8, 8.1 and 7.Android 5 and 4 were tested via the Android Studio Emulator and they didn’t work but I assume they would work if I actually had a device with those versions.While 8 and 8.1 doesn’t work on the devices, on 7 it did work just fine.I also got my hands on an android 6 device and it also worked on that.So the problem is isolated to just Android 8/8.1.
Also, is there anything more than enabling developer mode on my phone needed to be done?
As I already have it turned on for usb debbuging and that’s pretty much it.
I’m gonna plan to buy a play console account earlier then, I guess.
Do you have any sort of other things that I could try meanwhile?
We would need to see the device logs and the specific error that you are seeing. Please test on Google Play, that is the typical development flow.
I have actually started working on it from scratch and meanwhile I just messed with my version number and stuff and now it actually works on android 8.1 and I am pretty sure it will on 8 too!
So I think case is closed for now.
Thank you so much!