The problem is actually a feature of some routers. It is called lan isolation. It allows you to keep certain network ports / devices isolated from others.
Depending on your specific router (need more info) the configuration can be quite different. Essentially you need to put all you ether net ports and wifi connection into the same lan or disable isolation of the different connections.
Have a look at this doc
This feature is disabled by default. If it is enabled, wireless stations cannot communicate with each other or with stations on the wired network.
Based on your comment I went and looked at the manuals for the two devices you have. I think this is less a problem of Lan isolation settings, and more a routing problem between devices.
In the following sections.
4.6.4 Wireless Advanced
Choose menu “Wireless → Wireless Advanced”, you can configure the advanced settings of
your wireless network.
Enabled AP Isolation - This function can isolate wireless stations on your network from
each other. Wireless devices will be able to communicate with the Router but not with
each other. To use this function, check this box. AP Isolation is disabled by default.
If that does not resolve the problem.
It might also be necessary to do some routeing configuration on your devices.
4.12.2 System Routing Table
Choose menu “Advanced Routing → System Routing Table”, and you can views all of the
valid route entries in use. The Destination IP address, Subnet Mask, Gateway, and Interface will
be displayed for each entry
You may need to disable dhcp server on this device and set it up with a static ip address, and route to your actual router. On your router you would set up a static ip address to this device. This would let your router do all the dhcp set up for the whole network.
Have a look at this section of the manual.
3-3 LAN (Wired)