Hello,
This issue is most likely due to Server Configuration errors or User Customizations in the include/form.php File. The Form Processor uses the PHPMailer Library which is the leading mail library and Our Form Processors have been developed and improved continuously for the last 5 years. So, the issue is not necessarily due to the Form Processor included.
We have tried submitting the Form on your website and we are receiving a 500 Internal Server Error which you can also check on your Browser's Developer Console after trying to submit the Form. Please consider adding the following code at the very top of your include/form.php File:
error_reporting(E_ALL);
which should display all the possible errors. Please notify us about the Error Message you see, after going through the process above, so that we can provide you with more assistance on this.
Hope this Helps!
Let us know if we can help you with anything else or if you find any further issues.