Thanks for sharing the details, @phcaraujo!
Depending on how HappyForms shortcode is added to a pop-up and when pop-up is set to show up, it can fail loading HappyForms scripts that are necessary for submissions to work. Sometimes this can be caused by third party plugins related to site optimization that try to remove scripts printed on page in an effort to optimize page.
If you decide to reach out to us on support email we shared earlier in this thread and share your site URL, we’ll be happy to have a closer look and see if that’s the case.
Just a heads up – we also have built-in form popups in upgraded version of HappyForms.
Let us know how you go. ??