Hey there, Thank you.
The issue is that our support on these matters are very limited. Our support with Sitejet integrations is focused on the Website Builder. The tips I mentioned are gathered information from other users that have had this issue.
Since your form works on the preview and the configurations seem right, I need to advise that you contact the cPanel support on this matter. We do not have access or qualified knowledge of their system. But please keep us updated here when this issue is resolved to help others as well.