My sites were on HTTP only and I used the normal embed script:
It worked fine. However when I switched to SSL (HTTPS), all the forms disappeared.
Trying to fix this, I installed a Mautic installation on another domain on my server, created a form and inserted the code, it did not appear.
So I opened and account on Mautic.net, created a form and embeded the script above and it showed.
The only thing I can think of is that when the forms are not loading when being loaded on HTTPS on the same server, no matter what the domain address is.
All SSL certificated were installed in cPanel using Let's Encrypt SSL.
Thank you kindly for your help with this.