OPNsense backups contain a special character, in this case “:”. Which while most operating systems tolerate it causes an issue with the Windows NextCloud client and it is unable to sync. The developer has a very good point in that this isn’t a OPNsense issue, but a NextCloud / Windows one for not respecting, or being able to deal with special characters. However, all is not lost, there is a tiny modification you can make to one file on the OPNsense server to make everything OK!
First log into the shell on the OPNsense box (option 8 on the console GUI)
If you don’t have an editor installed you can use vi, or you can install nano
pkg install nano
Open the file
Change line 132 from
$configname = 'config-' . $hostname . '-' . date("Y-m-d_h:m:s") . '.xml';
This changes the “:” to a “-“, but you could change this to anything you like. Save the file, job done!
$configname = 'config-' . $hostname . '-' . date("Y-m-d_H-i-s") . '.xml';
Remember it is likely this will get overwritten with updates to OPNsense so I recommend you check the file after every update!