When having an issue trying to add a smart plug to your hub you may need to reset it to clear out any old configurations.
To reset the smart plug you will need to do the following.
1) Unplug the smart plug from your outlet.
2) Press and hold the button on the Smart Plug for 15 seconds.
If it’s done correctly it it should flicker twice after every second.
Example: flicker, flicker, pause one second, flicker, flicker, pause one second.
From my experience you may need to try this 2-3 times to get it right. By then your allowed to add the smart plug to your hub.