Metadata json html

[drhus]

how to add metatype json or html, it is in both doc https://standardnotes.com/help/67/how-do-i-specify-a-custom-date-for-a-post-or-set-the-canonical-url and app/controllers/posts_controller.rb but i don't seem to get it to work example publishig

--- 
metatype: json	 
--- 
{
"name": {
  "first": "some data xyz",
  "last": "some data"
 }