Hello,
I’ve checked popup at your website and it seems to work
https://www.dropbox.com/s/avmdyu6outquh2o/Screenshot_11.png?dl=0
Have you got “Empty or invalid email” error after entering email second time?
By default “Email error message” and “Email exists error message” text is set to “Empty or invalid email”.
https://www.dropbox.com/s/v3e22nv36qvf6mx/Screenshot_12.png?dl=0
This is done for security reasons. You can change these settings if necessary.
Best regards,
https://supsystic.com
Dante