How to eth0(from router) -> raspAP -> eth1(usb adapter) -> external AP

[crbyxwpzfl]

Hi

(Edit:
is it possible to use raspAP to create a subnet of eth0 on eth1.
or is it better to use systemd-networkd like here)

Tl;dr
RaspAP is connected to router via eth0.
I would like to use an external AP connected to eth1 via usb adapter.
Instead of hosting the created subnet on built in wlan0.
And therefore not use rasspberrys built in wifi.

Currently RaspAP is set up as an AP using wlan0 and I use my external AP in wireless Extention mode.
This works great RaspAP creats its own subnet and the external AP works great to extend the wifi range.
But sometimes the the hotspot goes down. I do not know why.
I heard that the built in wifi ot the rasspberry is not the best.
So I thought I can just connect the external AP to eth1 via a usb-to-ethernet adapter and just dont use the built in wifi.
Currently I use ping to detect when this happens and use
'sudo /etc/raspap/hostapd/servicestart.sh --seconds 3'
to restart the hotspot.

I already tried to just switch wlan0 to eth1 in hotspot - basic settings - interface.
but this doesnt seme to work.

I found this issue #382 but do not realy know what he does in his solution.

Im new to networking and do not understand much of it jet.
So this perhaps does not make sense.
Anyway im very happy for any help or tipps.
I really like this tool and for its ease of use really great work! thank you!

Thanks in advance
Flo

Additinonal Info:
Rasspberry Pi 4b Rev 1.4
RaspAP v2.6.4