Friends Access Not Working

I have invited a number of friends and given them full access to my server.
They have created accounts, but none of them can see my server or access its contents.
Is there perhaps some common mistake I am making?
Thanks,
Nick

Start Here: https://support.plex.tv/hc/en-us/articles/200484543-Enabling-Remote-Access-for-a-Server

Then there is also the Troubleshoot page: https://support.plex.tv/hc/en-us/articles/200931138

And then once Remote Access is working properly, here is the page on sharing your server:https://support.plex.tv/hc/en-us/sections/200295083-Server-Sharing

@nickdunc said:
I have invited a number of friends and given them full access to my server.
They have created accounts, but none of them can see my server or access its contents.
Is there perhaps some common mistake I am making?
Thanks,
Nick

is your server available via remote access ?