Why won't my TP-Link Tapo smart plug work on the guest network?

The short answer

Cannot be set up on 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

Setup fails on guest networks.

Source: Manufacturer documentation

Try these, in this order

• • During setup, turn 5 GHz off on your phone or temporarily switch the phone to the 2.4 GHz network name.
• • Stand next to the router while pairing, then move the plug to where you want it.
• • If your router has separate band names, use the one ending in 2.4G.
• • 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

Never for this. It's a setup step, not a hardware fault.