Please help. 

I bought a pack of Tapo smartplugs off of Amazon with a smart bub

I have installed the Tapo app and configured the hub, one smartplug and a motion sensor. All work in the app. I have linked to my Amazon Alexa account and the Tapo items are listed and able to be controlled from within the Alexa app. Cannot get the plug to activate using voice command. 

I have unlinked and relinked and still no joy. 

Please tell me what I'm not doing before I send it all back. 

Thanks. 

Rob.