I’m not sure exactly what you mean by “modem”. Modems can’t interact with SONOS. If this is a “Gateway” that provides the modem function, along with a “Router” and “WiFi access point”, the easiest method is to give the new WiFi access point the former “SSID” (WiFi name) and password.

Hi

If you changed a “Modem” as you call it that also acts as a router to provide WiFi you’ll have to update your Sonos network. Most likely as @buzz mentioned the SSID (network name) and/or password has changed. The people who install those devices typically don’t do more than make sure your cell and/or computer connects to the internet. 

In the Sonos app go to Settings > System > Network > Update Network 

This little “glitch” is similar to having a locksmith to change the door locks while no one is home, then he throws the new keys on the kitchen counter and walks out, locking the doors behind.

Sorry should have been more informative than that 

We got a new modem and router. The said and password are the same as the old system 

Thanks for the clarification….

You still need to follow the directions in my first post. If that doesn’t resolve the issue then please post back for more assistance. 

The router WiFi needs to be 802.11b/g/n compatible and try it using a security mode of WPA2 personal rather than WPA3.. Also maybe double check the WiFi SSID/Password credentials again (they are both caSe SenSiTivE).

When changing the router you need to renew the IP addresses of everything on the network. Usually its easiest just to reboot everything.

This comment is just for future reference and it’s not the Sonos suggested way. However. It works! We also assume we’re talking about a protected/secure network.

Remember that the router or a router/modem combo are just pieces of hardware. The router in either configuration broadcasts the SSID secured by a password that clients recognize then use to connect and receive the WiFi signal to access the internet.

Clients have no idea what brand or model of router is sending the information. Clients see every SSID within range but only connect to the one with the appropriate password. Another word to designate the SSID and password is “Credentials”. If the client doesn’t see the correct “credentials” being sent by a router it won’t connect to that router. 

I change routers when needed. Either because I’ve switched to another ISP, the equipment is outdated or I just want to upgrade to the latest tech. Regardless of the reason I do the following…

Power down any hardware (client) that uses WiFi. In the case of Sonos I just unplug the units. After all clients are powered down I then take down the old router or router/modem combo. I setup the new router to broadcast the same Credentials as the old unit did. 

The first device typically to connect is my cell phone. Since the credentials are the same it automatically connects.
Fast forward to Sonos. I plug in one Sonos product and launch the Sonos app on my phone. I select “Join an existing system”.  Since the router credentials are the same Sonos connects. This connection is no different than if the power had been loss due to a storm and later was restored. 

Next I plug in the remaining Sonos units and within a few minutes everything is as it was before I changed routers. 

NOTE: The key to this procedure is to power down (unplug) Sonos units before shutting down the old router. Then follow the steps outlined above.

See if your wifi is using WPA2 and 3 and if it is disable WPA3, a recent update seems to have screwed up some speakers ability to work with it.