I didn't have access to the original email address at that point, and went on with another email without the knowledge it would change.
Is there any way to undo this and set the original email address as the main Sonos account?
Best answer by jgatie
Specifically this part:
You can also change the email your Sonos system is registered to at a later time through the Sonos app.
Using the Sonos app for iOS or Android: Settings > Advanced Settings > System Registration > Change Sonos Account.
Using the Sonos app on Mac or PC: Select Help > Sonos System Registration > Change Sonos Account