This page consists of screenshots from the Subscription Form Design – Error Message Screen in Coming Soon Booster WordPress Plugin.
This gives an idea about how to configure Error Message Settings. You can easily customize the error message which has to be displayed to the users, if they provide incorrect email address while subscribing to your website.
Using Error Message Settings, you can provide content for Error message which you would like to display when user’s email address is incorrect. You can also customize the Color, Font, Background, Margin and Padding for the error message.