Hello, I have already answered on another thread, anyway: on my phone (LG D605) the app does not install because of the SIP VOIP service missing. This service is required by RRC Nano Server!
Searching on the internet, it seems that many branded Android devices (from Samsung, LG, Motorola, ...) do have SIP disabled or even removed.
I have verified the missing services using this free app:
https://play.google.com/store/apps/details?id=app.akexorcist.udevicefeaturesThis reported SIP and SIP VOIP services not available on my phone
. Maybe this is your problem too.
Ciao
Mauro IK2WPO