URL to your Customer's Canvas instance.
Typically, you do not have to specify this URL explicitly. If you add
id="CcIframeApiScript" to the script tag which links the
IframeApi.js, Customer's Canvas automatically detects this URL from the script source. However, if for any reasons you do not want to use the id in the script tag, you can use this property to specify the URL to the Customer's Canvas instance explicitly.