I can connect my laptop to the CPE210 using an ethernet cable as per instructions (set laptop address to 192.168.0.1, connect to 192.168.0.254).  The web pages all look as described.

I configured the CPE210 as AP, with IP address 192.168.1.9 and WPA-PSK security.  I set on my router (an ASUS RT-AC68U) a fixed address in the DHCP server for the CPE210, using its MAC address to set IP 192.168.1.9.  (I double-checked the MAC address several times, both on the device label and on the 192.168.0.254 web page.)  I have a number of such fixed addresses set up on my router and they all work without trouble -- laptop, desktop, wired NAS, printer, cooktop (!), etc.

After disconnecting the CPE 210 from my laptop and reconnecting it, with the same ethernet cable, to the router, then booting it up, I can see the wireless network it is hosting and connect to it with my phone or laptop (it correctly handles the WPA-PSK security),

BUT: that's just local: there is no internet connection and the ASUS router does not register the presence of the wired CPE210 device.  So the CPE210 has set up its subnetwork, but it is not itself on any network -- in particular, I cannot connect to 192.168.1.9, its assigned IP address ("unreachable").

I've reset the CPE210 and gone back through these steps twice, just in case -- result is always the same.

Since everything else works as advertised, I must be doing something wrong.

Any suggestion?   (I have 3 weeks left to return it if I cannot make it work ;-)