SP Page Builder - Form Builder doesn't send the FOrm

Hi, I've problems using the Form builder in SP Pagebuilder Pro. It simply doesn't send the form. I entered the correct recipient email but it doesn't send the form. I checked the Joomla PHP Mail settings and they are correct. I even clickted on the "send test mail" button in the Joomla settings and that worked perfectly.

Any idea where I should search for the problem?

Thanks and cheers