Create a course. Create a External Tool activity. In the activity settings, use the following for the Launch URL: http://www.imsglobal.org/developers/LTI/test/v1p1/tool.php Take note of both the course ID and the External tool instance ID (in the mdl_lti table). Craft this URL: http://yourmoodle/mod/lti/return.php?course=X&instanceid=Y&lti_errormsg=Testing&unsigned=1 Replace X with the course ID Replace Y with the LTI instance ID After navigating to that URL, you should see the LTI activity instance name as a heading with some text below it. Now craft this URL: http://yourmoodle/mod/lti/return.php?course=X&instanceid=0&lti_errormsg=Testing&unsigned=1 Replace X with the course ID After navigating to that URL, you should no longer see the LTI activity instance name as a heading. Instead, just the error text.