My apple tv is connected to the internet but I am having problems with the mirroring it to my iMac, the icon shows up but won't let me turn on airplay mirroring. I have the newest imac and apple tv.
First off check they are on same network and apple ID and you have home sharing on.
Can apple TV 'see' your library in Computers?
Reboot ATV with all cables out for 30 seconds and reboot router.
Post again it this basic elf fix does not help.
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