Hi, I'm still having this issue.
Unfortunately, it looks like the ca-certificates-mono package is unable for me.
Code
root@openmediavault:~# uname -a
Linux openmediavault 4.9.0-0.bpo.3-amd64 #1 SMP Debian 4.9.30-2+deb9u2~bpo8+1 (2017-06-27) x86_64 GNU/Linux
root@openmediavault:~# sudo apt-get install ca-certificates-mono
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Unable to locate package ca-certificates-mono
root@openmediavault:~#Am I missing something here?
Thanks again for this, been looking for this exact backup solution!