You can either use the javascript mode to insert the cancellation link, or you add the code - which is visible at the module configuration - into your template.
Both features does allow you to modify the output of the hint box.
With the Javascript Mode you do not need to edit your template. The invoice cancellation box will appear automatically!
Javascript Mode
Edit the file
cancelbox_template.php
. The file can be found in the module directory.Manual Mode
You can copy & paste the template code from the text box at the module configuration and insert it in the view
viewinvoice.tpl
. Modify the code as you want.