[Ring] Software update error

[Arlen]

On Linux Mint 18.3, receiving this error when attempting software 
manager updates:
The repository 'https://dl.ring.cx/ring-nightly/linuxmint_18.3 ring 
Release' does not have a Release file.Data from such a repository can't 
be authenticated and is therefore potentially dangerous to use.See 
apt-secure(8) manpage for repository creation and user configuration 
details.Failed to fetch 
https://dl.ring.cx/ring-nightly/linuxmint_18.3/dists/ring/main/binary-i386/Packages 
404  Not FoundSome index files failed to download. They have been 
ignored, or old ones used instead.
   I had received this error after attempting the automatic update of 
Ring, through software manager. I noticed only the daemon had been 
installed; not the Gnome client (that had been removed).
   Uninstalled Ring completely and removed the repository. Reinstalled 
(My previous post makes reference to this, as there was a little problem 
with the package name.)
    All seemed well until Linux Mint tried to refresh the update 
manager. Same error message is occurring again.
   I am somewhat new to Linux, so please be clear (and kind) :-)

Arlen