Why is a friend's shared server "offline"?

A friend of mine has an account (with a Plex Pass) and has invited me to have access to one of his libraries on his server. I got the email invite, and his server shows up on my server drop down list, however it shows as Offline or Unavailable. His server is up and running, he has the latest software version, and has remote access enabled. What can I do next to troubleshoot? How can I get his server to show up as Remote or Online with the green light?

Thanks!

Has your friend confirmed that they can access their own server remotely?

REF: https://support.plex.tv/hc/en-us/articles/200931138-Troubleshooting-Remote-Access

We looked on his mobile this morning and it didn’t look like his phone had remote access, either. Same issue, server shows up as Offline, but he says his server is running at home. My guess is that the link you posted holds the answer to this, though it will take some time to go over to his place to troubleshoot. I’ll update when I can. Thanks for your response!