First, ensure that the outlet or fixture that the eco4life Plug is plugged into isn't controlled by a switch (such as a light switch or power strip.) If so, make sure it is turned on.
Next, try and power-cycle the Plug by removing it from the outlet, waiting at least 10 seconds, and then plugging it back in.
If this is a one-off case, you can also try to setup the Plug again. Start by removing it from the eco4life app by selecting the Plug from the Home tab. Then press the Settings icon and choose Remove Device at the bottom of the page. After removing the eco4life Plug you can add the product again by following the eco4life plug setup guide.