YorkshireLion- You want the switch AFTER the Gateway Deco, not connected to the Router. Reconnect & repower the Decos starting with the 1st (Gateway) and you should be all set.

Francois... modem > Deco > Switch. The wired switch connected clients now are able to see and connect to the Deco's router. Enjoy! Peter

Nielsvg Your Popcorn Hour A300 was connected to your prior router. Most likely the credentials on your new Deco M5 are different (SSID - Password - Security).... so go into its settings and look for...