Smart devices are set to work on the 2.4 GHz frequency and will not connect and work on 5GHz. Even though 2.4 GHz carries less information, it has better range than the 5 GHz frequency band. The problem, however, is that many of the newer models of routers come with simultaneous 5 GHz and 2.4 GHz bands, called a Dual Band Router, and the 5GHz is quicker and tries to connect to the devices, thereby preventing them from connecting.
In order to enable linking, a seperate 2.4 GHz band is required, or the 5 GHz band needs to be temporarily turned off while linking. During the linking process, both your mobile device and your smart device need to connect to the same 2.4 GHz signal.
You do not need to disable the 5GHz band if you can separate the two bands by logging on to your router, and through the settings, changing the name (SSID) of each band. i.e mynetwork2.4 and mynetwork5 Then, simply connect to the WiFi name allocated to the 2.4GHz band on your phone