@Calmodulin 

The only way to add the email account is to have the Deco app loaded in the phone, log into the Deco app as an admin, and enter the email you want. The Web UI login does not have that ability.

Based off of that different thing that may have happened, for now, I would recommend removing the account by tapping the three vertical lines to the right of the email. Look at the top of the screen to make sure you are still logged into the Deco app as the owner and it's your email. The next thing I would do is to change the password for your TP-Link account by tapping on your email up top on the same screen.