I would perhaps just reset it and try again and see if the issue persists. Note the 2.4Ghz SSID password is case sensitive.

Hi ken, thanks for your reply. I already reset both router and Sub many times.

I even reboot my iPhone and iPad...

Ah okay, I appreciate something is not quite right .. but did you try cabling it to the router just to see if that gets it setup?

Thinking ahead, if you can get the Sub setup (when wired), then you can perhaps submit a system diagnostic report and post it’s reference back here for Sonos Staff to perhaps take a look for you.

Hi, I also try that alternative but after a long wait the app says that it cannot find the sub.

I think that there a communication problem with my router, but I don’t want to change the settings since all the rest works perfectly.

It might be your router is not able to allocate any further IP addresses - check the DHCP server settings.

DHCP server is enabled. Should I check anything else ?

...and are there addresses still available on the subnet? What are its parameters and how many devices are already connected?

the router supports up to 253 IP addresses. There are currently 13 devices connected.

I can’t see a reason - perhaps it’s best to contact/chat to Sonos Support and explain the things you’ve tried and see what they say. Here is a page link where you can contact them:

https://support.sonos.com/s/

thanks a lot Ken. 

i noticed that they are not reachable at this time of the day in my time zone. I hope I will be able to reach them tomorrow...

Yes, as it’s a weekday, I think you should be fine.

Hope you get it sorted.

Just a couple of further things that have ‘just’ occurred to me - have you checked that the S2 App is upto date? - perhaps just check for any updates.

Also some users here, in the not-too-distant past, have reported setup issues with Apple iOS 14.2 and problems with Apples “Private Address” feature. If relevant, then update your iDevices. 

The “Private Address” feature can be ‘temporarily’ switched off in the Wireless connection properties in the iDevice "Settings/WiFi network”.

Everything is updated. I switched off the “Private Address” feature but the problem remains (I rebooted everything again).

However, I managed to connect the Sub to my guest network. This means something I believe, but still I should be able to connect to my private network like the other 3 Sonos devices. Right ? 

Well that points to a problem with the network, rather than the sub - can you perhaps describe/outline the network setup - type of router/switches etc?

I also noticed that my ARC connected to the private network is the only device with a static IP address. Is this normal ?

In the Sonos App "Settings/System/Network/Networks” it will show you which WiFi networks are in use for your existing Sonos setup - perhaps see what that shows too. 

There is only 1 in use. Can I add more ?

It will usually only have a static IP address, if you have reserved it in your routers DHCP reservation table - it’s actually a good thing to reserve all your Sonos product IP addresses - even moreso as the system grows larger as it will help with system reboots following Sonos updates.

The IP address was given automatically by the router

the private network is a tri-band and maybe this is creating the issue. As mentioned before, I am not keen to change the settings which are OK for all connected devices including the Sonos Arc + ONEs

Only if you are using a Sonos ‘Move’ portable speaker. 

Note: you can change the current wireless network by wiring one Sonos device to the router and switching the system over to SonosNet - then change the Wireless credentials in “Settings/System/Network/Wireless Setup"

To check a system is running in SonosNet mode goto ‘Settings/System/About My Sonos” and the wireless mode next to each device will show as WM:0 rather than WM:1 (which is WiFi mode)

The Sonos products WiFi network requirements are shown HERE. The 2.4ghz band ideally needs to support 802.11 b/g for setup purposes, but presumably if it worked for the Arc then it should work for your sub too - that’s assuming you haven’t changed the settings.

I solved it ! I set my private network to single band (2.4GHZ), connected the Sub and then set back the previous settings (tri-band).

Thanks for your patience and support.

Ah that’s good news - happy to have helped (a little) and glad you’ve got it sorted.