HI,

Im in the same boat. Ive just puchased a new Amp and each time i try to add it to my system it goes to update then an error code appears. Then the amp just disapears from the system. Its brand new! and i can never get through to anyone to sort. Considering returning this asap.

Try wiring your amp directly to your router. Also, try to use the desktop app when you get to the point of updating the firmware.

Do try the Ethernet option, if you can get it working that way try removing it.

https://support.sonos.com/en-us/article/sonos-led-lights

Flashing white

The Sonos product is powered on and booting up.

When a Sonos product is connecting to WiFi, the status light will also flash white while it’s waiting to connect to the network.

Keep in mind the return window for new purchases. Verify it is showing you the correct country by scrolling to the bottom and looking in the left corner.

https://www.sonos.com/en-us/legal/terms#legal-terms-sale-returns

Same here - 

Have plugged directly into router, and tried resetting by holding down the join button (∞) whilst powering on. Tried numerous times, swapping out internet cables from known working devices, all with no change in status. Amp is one month outside of warranty. 

Very difficult to get help through Sonos with 60 minute wait times.

Thinking of contacting the Australian consumer protection and making a complaint