Make sure that your phone software is up to date. Also, make sure that you are using the new Owlet Care app. If your using an iPhone you should be running on the latest update version. Make sure you are connected to a 2.4 GHz WiFi speed. The Owlet does not support the 5.0 GHz WiFi speed.
Perform a full power cycle of the base station by unplugging it for 3 minutes. Plug it back in and reset the sensor. You can find out how to do that here.
Open the app, go to the Account tab in the bottom right corner and scroll down to the bottom.
Select "Add Device" within your app, and follow the instructions to register the base to your app.
(If you still see your Smart Sock connected under "My Devices," continue with this step and it will override the old connection).
If this does not fix the issue, please provide a proof of purchase. The Owlet comes with a 1 year warranty from the date of purchase. Also, include your mailing address & phone number.