Pass deprecated course keys through

lms/djangoapps/django_comment_client/base/views.py

@@ -182,7 +182,7 @@ def _create_comment(request, course_key, thread_id=None, parent_id=None):
         'anonymous': anonymous,
         'anonymous_to_peers': anonymous_to_peers,
         'user_id': request.user.id,
-        'course_id': course_key,
+        'course_id': course_key.to_deprecated_string(),
         'thread_id': thread_id,
         'parent_id': parent_id,
     })