Hello,
Thank you for choosing our plugin.
I’ve checked the popup at your website with my email, everything work well.
I suppose you’ve entered the same email several times. User can not sign up twice because you already have the subscriber with this email in the list of the subscribers.
You can change error message in Subscribe settings
https://www.dropbox.com/s/kdojqr72ip6y2h8/Screenshot_27.png?dl=0
but we don’t recommend this due to security reasons.
Best regards,
https://stagging.supsystic.com
Dante