@JayBird1972 

If you are running into  issue when set up smart plug with mesh router device, please make sure Tapo APP is up to date, and here are some steps to try: 

• Try to turn off the Mesh feature when set up KP400 smart plug
• Turn off WiFi6 or 802.11ax, Kp400 connects to 802.11n 2.4Ghz WiFi  ( you may turn off 5Ghz as well temporality when set up smart plug)
• Check if main router' security type is WPA3-only, if so, please change router's wireless security type to WPA/WPA2-PSK
• Ensure you have put in the correct Wi-Fi password during set up,here is a way to verify Wi-Fi password :

Go to Settings-> WiFi on your phone, Tap (or Long press  the router's WiFi name  ->Forget / Delete the network -> Reconnect to router wifi and it will ask for a password, will it accept your router password?

• Turn off VPN on your phone
• Try a different phone to set up tapo device if you have one

If the concern persist despite trying the above steps, may I know at which step the set-up failed, can I have a photo of the Error message? 

What is the model of and its IOS or Android version of your phone?  May I know the model of your EEor mesh system or have a link of the router, thank you