Have you tried deleting and reinstalling the Sonos app and rebooting your phone? You might also reboot your router.

Not clear what ‘connect to the Sonos app’ means. Do you reallly mean that when you run the Sonos app, it doesn’t connect to your system?

If that’s the case, the advice given above is a great start, but if it doesn’t work, knowing more about your setup would go a long way in helping build a mental image in order to do some more intelligent troubleshooting. 

Yes. I have done all of that— multiple times. There is an issue with the app I think that Sonia needs to address. I have several friends who have all reported the same issue recently. 

When I try to open the Sonos app on my phone, I get the error message:  “Unable to connect to Sonos.”  I have tried troubleshooting following advice on the Sonos website. Nothing seems to work. 

I would perhaps just check/reset your mobiles network connection and ensure your mobile device is first connecting to your routers primary network and not a guest network or other WiFi access point and then try things again. If using an iPhone perhaps consider switching off ‘Private Address’ in the WiFi network connection properties, if that’s applicable in your case.

Another thing if using an iOS device is to ensure the Sonos App has access to the "local network" in the devices privacy settings.