Show message after sumit not working

Hi everyone!

I’m struggling to set up the Subscription Pop Up form. Despite having selected the option Show Message in the After Submit section, once a user submits its email, the form redirects them to the default MailPoet page instead of displaying my custom message.
Strangely, the issue is not happening when I’m testing the site while logged into my developer’s WordPress account, so I’m completely lost…

Any ideas?

Thank you in advance!

The page I need help with: [log in to see the link]