Adding Amchart Interface to WordPress API

I was able to find a solution here.

Add this to $args in setup.php

'show_in_rest'        => true,
'rest_base'           => 'charts'

Add this to the bottom of the setup.php file.
fistly, you’re registering the fields to get/set in the rest interface.
then you’re registering the specific meta data to the post_type = amchart

add_action("rest_api_init", function () {
    register_rest_field("amchart", "_amcharts_html",
        [
          "get_callback" => function ($post, $field_name, $request, $object_type) {
                return get_post_meta($post["id"], $field_name, true);
            },
            "update_callback" => function ($value, $post, $field_name, $request, $object_type) {
                return update_post_meta($post->ID, $field_name, $value);
            }
        ]);

    register_rest_field("amchart", "_amcharts_javascript",
      [
        "get_callback" => function ($post, $field_name, $request, $object_type) {
          return get_post_meta($post["id"], $field_name, TRUE);
        },

        "update_callback" => function ($value, $post, $field_name, $request, $object_type) {
          return update_post_meta($post->ID, $field_name, $value);
        }
      ]);

    register_rest_field("amchart", "_amcharts_resources",
        [
          "get_callback" => function ($post, $field_name, $request, $object_type) {
                return get_post_meta($post["id"], $field_name, TRUE);
            },

            "update_callback" => function ($value, $post, $field_name, $request, $object_type) {
                return update_post_meta($post->ID, $field_name, $value);
            }
    ]);

    register_rest_field("amchart", "_amcharts_slug",
        [ "get_callback" => function ($post, $field_name, $request, $object_type) {
                return get_post_meta($post["id"], $field_name, TRUE);
        },

        "update_callback" => function ($value, $post, $field_name, $request, $object_type) {
                return update_post_meta($post->ID, $field_name, $value);
            }
        ]);
});

register_meta('amchart', '_amcharts_html', array(
  "type" => "string",
  "show_in_rest" => true,
  "object_subtype" => "amchart"
));
register_meta('amchart', '_amcharts_javascript', array(
  "type" => "string",
  "show_in_rest" => true,
  "object_subtype" => "amchart"
));
register_meta('amchart', '_amcharts_resources', array(
  "type" => "string",
  "show_in_rest" => true,
  "object_subtype" => "amchart"
));
register_meta('amchart', '_amcharts_slug', array(
  "type" => "string",
  "show_in_rest" => true,
  "object_subtype" => "amchart"
));

The valid post body is:

{
   'post_type':'amchart',
   '_amcharts_resources':'resource list goes here',
   '_amcharts_html':'html content',
   '_amcharts_javascript':'javascript content',
   'slug':'_amcharts_slug', //or just use the response.id value as the slug if you do not set this explicitly 
   'title': 'title',
   'status': 'publish'  //draft, publish, etc 
}