Error with Deep Linking Response

[Sneakers82]

Hello, I'm using the pylti1.3-flask-example to learn how LTI applications work. Specifically I was following along with the tutorial written here: https://docs.anthology.com/docs/lti/tutorials/pylti13

I have the example installed in a Blackboard SAAS instance and am having a little trouble. When launching the application I successfully get to this screen:

However, after selecting an option I get an error message and the Deep Linking Content is not created in the Blackboard course.

The error message reads :
The LTI tool isn't responding properly. Please contact your administrator for help.
java.lang.ClassCastException: class java.util.LinkedHashMap cannot be cast to class java.util.List (java.util.LinkedHashMap and java.util.List are in module java.base of loader 'bootstrap')

Strangely enough, I do have the pylti1.3-django-example working including with deep linking content. I am a novice at this and have been studying the code differences between the Flask and Django example as well as the PyLTI1p3 library to get the Flask application to work.

I've compared the following outputs from the Flask application to what the django application is sending and they appear to be identical.
@app.route('/configure/<launch_id>//', methods=['GET', 'POST'])
@app.route('/jwks/', methods=['GET'])

I don't know why Blackboard is complaining about the deep-linking response. Any help would be appreciated. Thanks!