If you see the "Couldn't find valid settings for this link" error at the top of the screen after saving an assignment with a Classwork.com link in it, or have other issues launching activities, it often is a result of a misconfigured installation of Classwork.com as an "App" in your Canvas course.

Don't uninstall then re-install the App. That can cause Canvas to think it's an entirely different application and will break our ability to push scores to Canvas when the students complete work. 

Instead, edit the App Configuration and make sure it's OK by following these directions:

In Canvas, do the following:

Make sure that every field is set exactly as shown here (our consumer key is obscured for security reasons, but yours should appear).

Often what you'll notice is that the Launch URL is wrong, and contains "https://app.classwork.com/lti/config.xml" or something similar. Make sure it contains "https://app.classwork.com/lti/launch."

Also check that the domain is set to app.classwork.com.

And it's a good time to double check that your Privacy setting is "Public" which allows Canvas to send us the student's names (otherwise, they show up in Classwork.com as a long string of numbers!)