Dear Deco team,

Today I received my Deco M4 3 pack, and it has been a delight using the system so far. Currently, my main Deco is plugged in to another router (RT-AC1500UHP) which connects to the Internet modem through ethernet cable.

In Router mode, the system works flawlessly, but I want to try switching Decos to AP mode as I want to fully exploit my existing router. However, whenever I switch the mode, the network is still there but it will not connect to the Internet. Here is the screenshot (I set the SSID and password to the exact one by the old router):

Would there be a solution on this? Alternatively, if I continue using the Decos in router mode and keep the other router around, would it be possible to bridge the routers? My Asus router has WDS mode but it seems like I can't configure WDS on the Deco app.

My current diagram is: 
 

Internet --> modem (Dynamic IP) --[ethernet]--> ASUS router --[ethernet]--> main Deco --> other Decos (all wireless)

I'm very new to this field so all advices are welcome!

Michael