@farmstead,

What router are you trying to connect the device to?

If possible, you could try to connect the device to a guest network or another network that is only using the 2.4GHz band.

Oftentimes, there are settings specific to your router that are causing connectivity issues, such as the SPI Firewall, however this is normally limited to once the device is connected to your Wi-Fi.

Does your Smart Plug connect to your network at all? At what point in the Kasa app does the setup process fail?

If not, I would double-check to make sure that your network is secured using a compatible encryption method such as WPA2.

Lastly, as it is a common mistake, try performing a factory reset instead of a soft reset by holding the power button for 10 seconds rather than for 5 seconds.