2012 iMac – Target Screen Mode not working

[Beliblis]

Hi,

I've got a 2012 iMac (21.5") and a 2011 MacBook Pro (13") and would like to use the iMac as a screen for the MacBook.
Unfortunately the Target Screen Mode is not working. From what I've seen/heard so far, my iMac should be ok with it...

Could it maybe be the lightning cable? It's a new one – but it's not original Apple...
Or is my laptop too old? (Also: the laptop only has the onboard intel GPU...)

Thanks a lot!!

 

[Mr_Brightside_@]

The iMac is logged in, right?

 

[azentropy]

It has been awhile but it is pretty picky about the cable. It does have to be a lightning cable and not just a mini display port cable (which has the same connections).