Your systemctl output seems to have been chopped off a bit - can you tell what’s showing after the “Server has started and is listening…” text?
I want to confirm that the --webservice-port –webservice-interface` parameters mentioned in your linked instructions (and here) are being used as expected:
By default Duplicati only listens on the loopback address (for security reasons) - since you’re looking to open it up to the network, do you think you’ll need the --webservice-password parameter as well?