Subscribe popup not working

Hi, I’m facing problems with the subscribe type popup.
I can create the form and it previews ok in the WordPress admin panel, but when it shows up in front end it’s missing some modifications.
For example I change the placeholder First name but it keeps showing First Name, I change the value of the submit button but no effect.

I tried removing cache, open the website in private mode but no effect
I have bought an extension but it’s unusable if I can’t create a form as I like !

Please help.