Why won't my Apple TV 4K work on the guest network?

The short answer

AirPlay from your phone fails across a guest network. Guest networks deliberately stop devices from seeing each other. That is exactly what this gadget needs to do, so it fails — as designed.

What's happening underneath

Casting breaks.

Source: Manufacturer documentation

Try these, in this order

• • Put the phone and the Apple TV on the same Wi-Fi name.
• • Turn off any isolation setting on the router so the two can see each other.
• • Plug the Apple TV into the router with a cable if one is within reach.
• • Check the signal where the gadget actually lives, not where you're standing.
• • Move the router off the floor and out of any cupboard before buying anything.
• • Put the gadget and your phone on the same Wi-Fi name.
• • Restart the gadget before the router — it is quicker and it fixes more.

Setting it up again properly

• • Stand next to your router while you set it up, then move the gadget to where it lives.
• • Put your phone on the 2.4 GHz network name for the setup, or use one name for both bands so the phone can follow.
• • If your router splits bands into two names, turn the 5 GHz one off for five minutes rather than fighting it.
• • Turn mobile data off on your phone during setup — some apps quietly use it and never find the gadget.

When it's worth spending money

Only if 4K streams buffer with a strong signal — then it's your broadband speed, not the box.