Try connecting it with an ethernet cable, then check for updates. There was one released this week. remove the cable after doing this and if it still fails to connect, do a reset and add the speaker again while still connected with the cable. 

If it still fails, give support a call ah have them look at a diagnostic. It it is a hardware failure, you may need to choose between an upgrade or using the speaker hardwired.

It might be worth double checking that the network meets the requirements as stated in the Sonos Network Requirements FAQ. Just in case there’s a mismatch in some of the system. 

Thank you both for your advice. I’ve downloaded the latest app version and managed to connect it directly to my internet using an Ethernet cable.  

Make sure you’ve not turned off wifi - toggle it a few times. Otherwise generate a diagnostics report and call Sonos support - the wifi card may have failed.