Hey @Ed_A,
The KP401 can only be initially setup in the Kasa or Tapo apps, other apps and integrations will be done for your account, rather than the device.
Which App are you using to setup your device? At what point in the setup are you having difficulties with?
FAQ: What Should I Do If I Fail to Configure my Kasa Device
First, make sure that the Tapo or Kasa app is up to date and try the setup after the update if there is one.
What is Your Phone Model and Operating System Version?
Also, make sure that you have also disabled any VPNs on your phone, as these will interrupt the setup. You may also consider disabling the Private Addressing feature for your Wi-Fi network. This is found in your phone settings and will cause your phone to be seen on the network as a new device each time it reconnects.