Hi all,
I Bought hex RB750GR3 + 2x cap ac RBcAPI-5acD2nD. I’m trying to run a capsman on this RB750GR3.
I saw few tutorials and configured according to them. At a certain step(Wireless tables–>CAP), however, I have a problem - the inability to select the interface. Description in the attachments. Probably I need to create an interface. The question to you is where and exactly what interface to create. Many thanks in advance for help 
What tutorials did you follow?
Here is the official wiki: https://wiki.mikrotik.com/wiki/Manual:CAPsMAN
If you want feedback, can you please share the current config?
/export hide-sensitive file=anynameyoulike
Remove serial and any other private info (like public IP).
Update: CAP interfaces are added dynamically, when the CAP registers to the CAPsMAN. Just follow the wiki.