Try unplugging the speaker(s) from power for a couple of minutes and reboot your router and phone. Also delete and reinstall the Sonos app.
I've done all that multiple times
Perhaps first see this link:
https://support.sonos.com/s/article/4948
Also ensure your mobile device is running Android 8.0 or higher, check for any Sonos updates, ensure the mobile is connected to same 2.4Ghz WiFi band as your Sonos products and maybe try a different DNS server on your router, such as the Google public servers 8.8.8.8 or 8.8.4.4.
Check there is no ‘security software’ running on the mobile device, or router that is restricting/blocking your online access, such as a VPN service, or firewall.
If still no joy, then go onto try a different mobile controller device, if you have one available.
Also check if you are using a DNS (Domain Name System) filter on your LAN, mine requires either careful tweaking or disabling for setting up some services.