Hello  @Tejiyas 

Please ensure correct Wi-Fi password is put in when set up your smart device

• How to Verify Router Wi-Fi password? 
  •  Forget router Wi-Fi on your mobile phone and manually input Wi-Fi password to verify router’s Wi-Fi password is correct.   ( Phone Settings > Wi-Fi >tap router's Wi-Fi SSID to forget network or Long press wifi name to delete the Wi-Fi profile)
• Turn Off VPN on the phone when set up  the smart switch

May I know when to reconfigure the switch, at which step the set up failed, and how about the led status on switch , is it Flash green or Red color? 

You could try to connect switch to a mobile hotspot wifi for a test, later reset it and relink it to router wifi. 

Hi  @Tejiyas 

• 'TPlink Smart XX' default SSID is for APP to find smart device and that smart WiFi has No Internet,  after it phone has connected tp tp-link smart wifi, go back to APP set up and APP will try to look for smart device. 

• Please follow APP instructions to set up the smart device, when app guides to connect to Kasa_Smart Switch_ XX SSID (smart  device default SSID is an open Wi-Fi without Internet access, it will be gone after smart device successfully connected to router's Wi-Fi)
• iOS: Go to the Settings page, click on the Wi-Fi  to connect to the Smart device’s Wi-Fi manually, then go back to app to continue set up

Android: Android phone will look for smart device automatically, if not or could not find  device,  manually connect to Smart device's Wi-Fi, go back to APP and continue set up.

• You could try a different phone to set it up if you got one. 
   

If still the same, may I have a photo of the error message, android or IOS version of your phone.