The following is the list of requirements for registering devices on rapyuta.io
Ubuntu(16.04 and 18.04) by default resolves the hostname to localhost. If you do change this behaviour on the host OS, roscore will not be able to start. A simple way to check if roscore can be started is to do
nslookup $(hostname) if it returns a DNS record you are probably good to go.
Ensure you install ros-kinetic-ros-base, or ros-melodic-ros-base, or above it.
Read about the device onboarding process, which consists of registering, setting up and viewing a device on rapyuta.io