Funbox 2.0 and WRP-300 Access Point Setup: SSID, Channel, DHCP, MAC Filtering, Connection Issues

Hi everyone. I have a Funbox 2.0 router from Orange on the top floor. On the lower floor, the WRP-300 device, set as an Access Point, is connected via a cable. I don't know much about networks, but by trial and error I set it up like this:
- I set a different SSID for the AP than for the router
- I set another channel (4 holes away)
- I enabled DHCP on it (it is also enabled on the router)
- I have disabled MAC filtering on my router

Everything started to work great, the devices see the AP and connect to it (via WiFi), there is good coverage. But there was a problem. As soon as a device is connected to the AP, the internet stops working on the computer at the top (connected with the cable to the Funbox)! A yellow triangle appears next to the network icon in Windows and the page is not loading. For the internet to work again, I have to disconnect the cable from the router to the AP and everything is OK.

If I plug back in, the internet works all the time, but only until a device connects to the AP via WiFi - then the internet on the computer goes down.

I don't have the strength for it anymore, so please give me some advice for a layman.

PS. I am a visual learner myself, so I prepared such a visualization to make it easier :)

as for me, both devices with DHCP enabled duplicate the same IP address in the network, so by default, when the AP after WIFI assigns a new address to the device, the same address is already assigned from the FunBox.

zenon90 wrote:

I turned on DHCP on it (it's also on on the router)

That's why the problem - turn off DHCP on this AP.
Leave the DHCP address assignment to FunBox.