Everytime I tried to add my RE270K (V1) WiFi Extender to Kasa, it would fail because it would not accept my admin password. 

The way I worked around it was to connect my PC to the RE270 and set the unit up in Cloud settings.

Magically, it appeared in Kasa.

However, that's not all.

I was able to control the plug with Alexa and Google Assistant but when I tried to control the integrated smartplug in Kasa, it again would require but not accept my admin password.

Looking in the extender's settings I saw that the timezone in the extender was set to Dublin.

Living in Eastern Canada, I changed the timezone to Toronto and then everything worked.

Hopefully this will help others who will be stuck as I was.