Hello,
We have just checked out your Website and as you have mentioned, the Form Processor is returning a 500 Internal Server Error.
Firstly, please make sure that your PHP Version is more than 5.6 or preferably the Latest Version.
Secondly, it might be possible that the PHP mail() Function is blocked by your Web Hosting Provider in order to to prevent SPAM. So, it is Highly Recommended to use SMTP Functionality for Forms as it ensures that the Mails are delivered securely.
Please check these 2 issues above and if you are still facing further issues, the please consider adding the .customjs Class to the .contact-widget Element and then following code at the very top of your include/sendemail-autoresponder.php File:
[ch_pre type="php"]error_reporting(E_ALL);[/ch_pre]
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.
Additionally, it appears that you are using a Very Old Version of Canvas. It is recommended to upgrade to the Latest Version of Canvas to ensure Plugins work more reliably. Moreover, support for v5.x or older will be very limited.
Meanwhile, do let us know if we can help you with anything else or if you find any further issues with Canvas.