@Chamywak Hello, 

May I know were you able to connect to router's 2.4Ghz Wi-Fi by manually tying in 2.4Ghz Wi-Fi password? If so, you could try some suggestions here: 

• Make sure Tapo app version is up-to-date 
• Check if main router' security type is WPA3-only, if so, please change router's wireless security type to WPA/WPA2-PSK
• Use numbers and letters only in router's wireless password (without special characters ) if possible
• Try a different phone to set up tapo device if you have one

If still the same issue, please help confirm some information here to help locate the issue:

1. Model of Main router &  a photo of wireless settings on main router:
2. Model of phone and its Android or IOS version: 
3. Tapo APP Version: 

4. A photo of the Error message on Tapo APP 

Btw, may I know your first time settings up this tapo plug? Tapo P100's hardware version, is it V1 on the back label? 

@Chamywak Thank you for your update. 

You may need to google the model of router to check if main router a dual-band or single band router. 

As there is some other settings need to be checked on  router, it is recommended to contact the router to verify settings above. 

@Chamywak Thank you for the update. 

May I have a photo of wireless settings on your router? What is the model number of your router?

Please also help confirm the information in my first reply to help locate the issue, thank you. 

@Chamywak   Thank you for sharing the update, glad to hear that plug connected to router now. 

Hello @Bakie 

Smart plug could connect to a dual-band WiFI router/ system,we have many smart device connected to Deco wifi in our office. 

While there is some cases , when router uses the same SSID and Wi-Fi password for both 2.4Ghz& 5Ghz, that may confuse plug during set up, you could temporarily turn 5Ghz off or use a different 5Ghz Wi-Fi name if set up failed.