Wouldn’t it be nice if Sonos just posted that on their support page instead of waiting on hold for an hour with customer support?

Thank you. Yes, I know. I called Sonos support and they told me to do just that. And it worked. 

I had this same problem. Try using the Desktop app instead of the mobile app. For some reason, that worked for me and took 5 minutes vs wasting 5 hours. 

Exactly. 

Thank you for the information! The desktop app for Mac has helped me update the new Sonos One SL. Then after the update, I can connect to that speaker from the mobile IOS app.