DIAGNOSIS The process is straightforward but has to be done in a specific order. The app sometimes assumes you know the steps.
FIX Here's the reliable way. 1) Plug the new node into power, but place it in the same room as your main router node. 2) On the main router, press and hold the WPS button for about 2 seconds until its LED starts flashing. 3) Within two minutes, press and hold the WPS button on the new node for 2 seconds. 4) Wait. The nodes will talk. The new node's LED will cycle and eventually turn solid white. This can take up to 5 minutes. Once it's white, you can unplug it and move it to your desired location.
IF THAT DIDN'T WORK Use the ASUS Router app. Go to the main screen, tap the "+" icon or "Add Node." The app will then guide you through the process, which usually involves scanning the QR code on the bottom of the new node. Make sure Bluetooth is enabled on your phone for this method.
HEADS UP Don't try to set up the new node from its final, distant location. Always do the initial pairing within 10 feet of the main router. After it's part of the mesh, then you can move it.