Canvas: How to fix a "Forbidden (403)" Error

First things first, don't delete the Classwork.com or TeacherMade app from Canvas in an attempt to fix this. Doing so can cause Canvas to get confused and refuse our attempts to send scores. If you need to fix the installation of the app as directed below, just edit it. Do not delete and re-install it.

There are actually two different Forbidden pages.

Forbidden (403) in Yellow

The first looks like this, and there are two possible causes.

The Most Frequent Cause of the Yellow Box 403 Error

The most frequent cause of this kind of error is that you've posted the wrong kind of link into your External Tool Assignment in Canvas. Either you've generated the Assignment with a Classwork.com Assignment delivery option, or you copied the URL from the browser toolbar or a Share link from Classwork.com.

To fix this kind of Forbidden (403) error, just make sure you use the Copy button to grab the Canvas-style link (which always has /lti/ in it).

Always use that link to paste into the URL field of the External Tool Assignment in Canvas (and don't click the Find button).

The Other Possible Cause of the Yellow Box 403 Error

The other possible cause of the yellow box 403 error is that you've copied the right link from Classwork.com, but pasted it into an "External Tool' Module Item in Canvas, rather than an Assignment in your course. The correct method to place a Classwork.com link is to create an Assignment, selecting "External Tool" as the "Submission Type" field. Then you can insert that Assignment into your courses modules if you wish. You will receive the yellow 403 error if you directly insert an "External Tool" into a module of your course, rather than first creating an Assignment then inserting that Assignment into the module.

White Screen With the App Menu Visible

The other Forbidden page looks like this:

This one implies there's a problem with the External Tool installation in your course, such as needing to recopy the consumer key and secret or possibly the launch URL. In those cases, the Classwork.com link (or Teachermade link if you're old school) that gets installed in the left-hand column of the course would also not work.

To fix that, you'll want to edit the External Tool installation in your course.

Click here to see directions for editing the External Tool settings in Canvas.