I am receiving a 406 error (The requested resource is only capable of generating content not acceptable according to the Accept headers sent in the request), I am not sure if this is because my request is incorrect or if the POST feature of this API is active yet?
Thanks for your question- it looks like you were seeing a 406 error because the POST feature of this API was not active. However, we've now updated the feature so that master pages can now be created via the REST API. If you attempt this request again, it should work as expected.
Hope this helps Addison- let me know if you run into other issues 🙂