Look at the URL in the browser screenshot above.
There is one major limitation on Synology – You cannot use the QuickConnect URL to setup the NAS even if you are local to it.
To perform setup, and be properly authenticated / claim, connect to it directly by its IP address http://192.168.254.158:32400/web
Now you’ll get the setup.
PMS has security built in. It won’t let anyone who is remote claim your server. When you use the FQDN (QuickConnect domain URL), it connects from Synology’s servers – and they are remote. This is the security doing what it should.
Once you’ve setup and claimed the server, you can use the QuickConnect button as much as you want.