This happened to me before I got onto PC. The way I solved it was to install an external apks installer, this is because the default android app installer absolutely sucks and it gives a lot of errors with no explanation. I don't remember what the apk installer I used back in the day was called, but you can just look it up easily.
Ok thanks. I found one that seems to work, as I can install other apps with it but it's saying that Mousegun isn't compatible with my phone. I'm not sure if it's the issue but my phone, while it has an arm8 (64bit) processor, is running an arm7 (32bit) version of android. If that is the issue, then I'll have to try again later if I get a better phone.