I saw that on my pone this morning, but I had no issues closing it.

Force close the app and relaunch to see if that helps. If it doesn't, try resetting the app.

https://support.sonos.com/en-us/article/reset-the-sonos-app

I was able to X out the ad on my iPhone but on the iPad you cannot. Tried force quitting, didn’t work either. I uninstalled the app and reinstalled it and for now the ad is gone. 

All of those options Saoud were attempted and didn’t work. Even tried changing the orientation of the iPad, splitting the screen - nothing worked. We’ve got a bug here :) 

You can block these ads if using a dns based network ad blocker like Pihole or Nextdns