The primary requirement for using Plex for Sonos is that the Sonos service for Plex needs to be able to reach your Plex Media Server to talk to it. That's what lets you browse your Plex Media Server library content in the Sonos controller application. So, what do you need to do?
Enable Remote Access
To allow your Plex Media Server to be accessed as needed, you need to enable Remote Access for your server. That's done under Settings > Server > Remote Access in Plex Web App.
In many cases, it will either already be successfully configured for you or the automatic configuration will work fine. Sometimes things can't be auto-configured, though, and you'll need to do something such as manually forward a port in your router/modem.
Successfully enabling Remote Access will give you the best experience with Sonos.
What if I Can't Get That Working?
Even if you can't get Remote Access successfully enabled, you'll still be okay. In this case, you need to be running at least version 0.9.15.0 or newer of Plex Media Server. When you do so and and don't explicitly disable Remote Access, then your server will still be able to set up a "Relay" connection, even if Remote Access isn't fully configured.
Our Relay feature allows a limited connection to be established to your Plex Media Server even if the normal Remote Access isn't working.
Tip!: Remember that you need to run Plex Media Server version 0.9.15.0 or newer and to turn on Remote Access in order for Relay to be available.
Related Page: Accessing a Server through Relay