User is getting 'Required parameter "tool_consumer_instance_guid" missing from LTI params' when installing Blackboard app

See https://hypothesis.zendesk.com/agent/tickets/6024

The user has admin permissions in Blackboard. We watched her delete and reinstall the platform using these directions: https://web.hypothes.is/help/installing-the-hypothesis-lms-app-for-blackboard-administrator-guide/. Her LMS domain appears to be correct (though it is a staging instance), and the settings she selected were correct.

Domain: https://bb-montgomerystage.blackboard.com
Email: robin.cook@montgomerycollege.edu

After installing, she opened a course, confirmed she was an instructor in it, and created a reading using the "Hypothesis" tool [as shown in our instructions](https://web.hypothes.is/help/creating-hypothesis-enabled-readings-in-blackboard/). After saving and clicking on the assignment to configure (Step 5 in our instructions), she received the error 'Required parameter "tool_consumer_instance_guid" missing from LTI params'.

In the console, the error was "Failed to load resource: the server responded with a status lti_launches:1 of 400 ()".

I've only seen this error in D2L installations when the admin has added us as an External Learning Tool, but hasn't also added us as a Tool Provider.