Hello,
Since your Form File: include/form.php (https://birdclick.co.uk/endonet/include/form.php) is returning a 500 Internal Server Error, it is an indication that this is a Server Configuration issue.
Please consider adding the .customjs Class to the .form-widget DIV and then the following code at the very top of your include/form.php File just after the opening php tags:
[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 further assistance on this. Thanks for your Patience.
Meanwhile, do let us know if we can help you with anything else or if you find any further issues with Canvas.