No, it’s not listed 
Yes, see below. Other details is listed in the same post.
No - guess i missed that. But, doesn’t work. Or - well, it works if i run it manually:
mono /volume1/@appstore/Duplicati/Duplicati.Server.exe --webservice-interface=*
I edited hostname (added a few, seperated with ; as suggested in the text), saved it, Ctrl+C, checked for other processes, and started the service through the Synology-solution. Same error, once again.
If i run it manually, it’s clear to see that i have the right connection to the backend, cause language is in danish (I’m from Denmark), and not english as is it on the sessions where it’s reporting the error after a few seconds.
I also tried to start manually again, and confirmed that the hostname-value was still defined (and it was).