Configuring Hotspot with Capsman - Interface selection issue

Hi friends,

I m struggling to setup the hotspot for my three CAPac access points that are managed by the CAPSman on the main router.

This is my hardware:
hardware.png
This is my interfaces:
interfaces.png
This is the bridge configuration:
bridge.png
And this is my CAPsMAN with the CAPs attached to it:
CAPsman.png
I followed the steps of various tutorials I found on google, but I do not understand what interface I should select during the Hotspot setup as I get an error of the following type (see below). Also, I would like to know if I can have my three AP’s under the hotspot at once, I mean, could I somhow group all the AP into one interface and then apply hotspot to this one, while still have the AP managed by CAMsMan?
error.PNG
Help would be so appreciated, I m really not getting this to work.