Section themes REST API unavailable?

[ihnat-s]

Any API tutorial on how to enable the new Page Sections would be really appreciated.

As for now, I am trying to enable them by creating a Master page as the first step and then assing Product Page Section (pages/product.liquid) to this master page:

POST /admin/master_pages.json 
{ "master_page": { "name": "Default", "sections": [] } }

But even this API request fails with HTTP 406 Not Acceptable and empty response. Please correct me if the workflow is not valid.

Thanks in advance.