I've had the same problem as everyone else.
Using a MBP running High Sierra I downloaded iMazing.
Following instructions many times, activation failed.
I then downloaded Apple Configurator 2 (v2. 2) from here:
That also failed.
In all previous attempts the Apple TV was connected to the MBP via USB + power plugged in.
Tonight I connected the Apple TV to the TV set - with HDMI & power cable attached as normal.
While Apple TV was connected to the TV set, I saw the usual "activation failed" on screen.
I then opened Apple Configurator 2 and tried to activate - that failed as usual.
However, leaving Apple Configurator running in the background, I opened iMazing.
I clicked "profile" and got an error message saying connection to Apple TV failed.
But at the same time, I suddenly noticed the usual "activation failed" suddenly vanished from the settings screen.
I disconnected USB from Apple TV, and now Airplay (using airparrot to mirror the MBP screen) is suddenly working perfectly.
I have no explanation.!!
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