If you have a student in a Google Classroom who says that they cannot access an Edpuzzle assignment and are getting the message "Please have your teacher add you to the classroom" it is likely the student was added to the Google Classroom AFTER the class was synced with Edpuzzle. The video linked below shows how you can update the list of students in Edpuzzle by re-importing the students.
Update Existing Classes in EdPuzzle