Smart-home device will not join Wi-Fi

Many basic Wi-Fi devices require 2.4 GHz and a specific setup process in the maker’s app.

Do not factory-reset a router speculatively or indiscriminately disable Wi-Fi security or a firewall. Get permission before changing someone else’s network.

Check the manual for supported Wi-Fi bands and the correct app. Install it only from the official app store or a verified manufacturer link.
Set up the device near the router. Ask the connection owner whether a compatible 2.4 GHz network is available.
Some setup processes need the phone and device on the same network. Guest networks can isolate devices; change network rules only with the owner’s permission.
Do not disable Wi-Fi encryption or open router ports speculatively. Record the model and setup error for help; never open mains-powered devices.

Test after each step and stop when the issue is solved. Checkmarks are not permanently saved.