Hi @RonaldT
Welcome to the Sonos Community!
The problem seems to be that your Boost is on S2 software, whereas your system is on S1.
Please disconnect your Boost from power and ethernet, then connect another Sonos device to that ethernet cable.
Power on the ethernet-connected Sonos device (if it’s not already on) and you should see your system come back online in a minute or two.
If that has worked, all we need to do now is get your Boost back on S1. Please factory reset the Boost. In the S1 app, select Settings » System » Add a Boost and follow the instructions. Once the Boost has added, “updated” and registered, you can then reconnect it to ethernet.
If none of this goes to plan, or if you still get the messages about S2, I recommend you get in touch with our technical support team, who have tools at their disposal that will allow them to give you advice specific to your Sonos system.
"Common sense is the collection of prejudices acquired by age eighteen." - Albert Einstein