Can't access my router admin page when using it as access point

I’ve an AR750S Slate and when using it in router mode I can access the UI admin page as expected ( but when I set it up as an Access Point I cannot access to it.

When doing the change the message that pop ups tells me to use the IP that my main router provides it, which according to Fing is, but I still can’t access it.

The only way I can access is to reset Slate back to router mode holding the button for 4 seconds.

Also I was hoping to have way to extend my home SSID like with an extender but using the ethernet cable as a source, is that possible?

I don’t want to have two networks in my home.

If you use in AP mode, you should be able to access it from, unless your main router has some setting prohibiting this, e.g. AP isolation.

If you set up as Extender (which is different from AP), you cannot access using the IP from main router, e.g., but rather, you should assign static IP (e.g. to your PC and access the router at