AP Mode Not working when its fed via a switch

Routers
1

I setup the GL-AR750S to use as access point, it works fine. The setup I tested is like, from my main router's LAN cable, I connected a cable directly to the WAN of the GL.iNet router while running the AP mode setup. Upon checking the wifi, I am getting the IP address of the main router subnet and internet is working well too.

But when in the same setup, when I connect the main router's LAN cable to a 4-port (unmanaged) switch, and take one cable from the switch to connect the GL.iNet WAN cable, it doesn't work, neither gets any IP. Please tell me why it doesn't like the cable from the switch (if I connect my laptop to the switch, I get the IP from main router and everything works though).

Regards,
IK

2

This should just work.

How about you do this: first reset the router to Router Mode and check if the router can get IP address from the switch. If yes, change to AP mode.