I can define a "Dummy" JSON course object and use Create Course REST API to create the dummy course.
But how about If I would like to create a course from another course template?
Or can I create a new course by copy the courses from another course by externalID without membership?
Thanks
I don't think you can do this with the REST API.
The create course does not have anything equivalent to the SIS integration TEMPLATE_COURSE_KEY or way to copy the content from course to course.
You would need to use a SIS integration.