Target display mode compatibility between Macbook Air(13 in. - Early 2015) and iMac(27 in. - Mid 2011)

Hi all,

I have a Mini Display port to Mini Display port cable recently purchased.

I have tried hitting Command+F2 on the target computer (iMac) in order to use it as an extended desktop for my Macbook Air.

Nothing pops up and there is no response from the computer.

The newest thunderbolt cable is quite pricy in my home country, and I am not able to afford it.

Is there any way I can force my iMac to recognise this MiniDisplayPort input? Like some third party software or something?

-Thank You-