Roon on Mac won't give up its server

I have been running Roon on a Mac Mini for a few years with no problems. I got a Nucleus One last week and it is running fine using my iPhone or iPad as remote. If I try to use Roon on Mac as remote I get - ‘Connect to your Roon Server’ page and can see a connect to ‘This Mac’ or ‘Nucleus One’ as options. The Nucleus One offer doesn’t work as it shows red - connecting flag and Connect button hasn’t come to life. Therefore, so far I am unable to use Roon on Mac as a remote.
Any ideas?

No offers of help or interest apparent here.

Problem was firewall on my Mac.

OK now.