@Mark_W The slide in connector with the black and white wires is not a neutral. In your case the power is at the fixture, and the neutral is at the fixture. Without the neutral you can not use a...

@Smakmauz I just got a email from KASA for a sale on the HS103P4 , they called it the New Version 15Amp

@matlocket Your Welcome Glad to be of help.

@matlocket swap the black leads, then it should work.

@CtrlAltDave Did you add the white wire from theHS210 to the neutrals, or did you remove one of the neutrals and connect it to the white wire on the HS210?

@Nickp001 Your welcome Glad to hear you got it working.