mini ipad 4 and IMAC

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I would like to control my IMAC with OS Sierra 10.12.6 by mini ipad 4 ios 10.3.3.

I tried but mini ipad remains with black screen and the message "Connection in progress".

On my IMAC it seems to be connected  because i see the open session.

What is possible to do, How can I resolve?IMG_5903.PNGSchermata 2017-09-21 alle 16.47.59.png