How to include META fields in Wordpress API Post?

First of all, you need to set the 'show_in_rest' property to true and 'supports' property should include 'custom-fields' when you are registering a new post type.You need to support 'custom-fields' if you want to include the meta fields.

Note that for meta fields registered on custom post types, the post type must have custom-fields support. Otherwise, the meta fields will not appear in the REST API. https://developer.wordpress.org/rest-api/extending-the-rest-api/modifying-responses/

function cptui_register_my_cpts() {    /**     * Post Type: Experiences.     */    $labels = array(        "name" => __( "Experiences", "twentynineteen" ),        "singular_name" => __( "Experience", "twentynineteen" ),    );    $args = array(        "label" => __( "Experiences", "twentynineteen" ),        "labels" => $labels,        "description" => "",        "public" => true,        "publicly_queryable" => true,        "show_ui" => true,        "delete_with_user" => false,        "show_in_rest" => true,        "rest_base" => "",        "rest_controller_class" => "WP_REST_Posts_Controller",        "has_archive" => false,        "show_in_menu" => true,        "show_in_nav_menus" => true,        "exclude_from_search" => false,        "capability_type" => "post",        "map_meta_cap" => true,        "hierarchical" => false,        "rewrite" => array( "slug" => "experience", "with_front" => true ),        "query_var" => true,        "supports" => array( "title", "editor", "thumbnail", "custom-fields" ),    );    register_post_type( "experience", $args );}add_action( 'init', 'cptui_register_my_cpts' );

Now, you need to register the meta fields using the register_meta().

add_action( 'rest_api_init', 'register_experience_meta_fields');function register_experience_meta_fields(){    register_meta( 'post', 'location', array(        'type' => 'string',        'description' => 'event location',        'single' => true,        'show_in_rest' => true    ));    register_meta( 'post', 'date', array(        'type' => 'string',        'description' => 'event location',        'single' => true,        'show_in_rest' => true    ));    register_meta( 'post', 'event_url', array(        'type' => 'string',        'description' => 'event location',        'single' => true,        'show_in_rest' => true    ));}

Note: The meta fields must be unique. Prefix your fields in ACF to make it unique.

JSON doesn't use single quotes to wrap a string. It uses double quotes. You are sending invalid JSON.

Now, if you want to create a experince post type.Use a JSON linter to validate your json. https://jsonlint.com/

Make a POST request to http://paathsala-plugin.test/wp-json/wp/v2/experience, with the fields

{    "title": "test",    "content": "testingfrompython",    "status": "draft",    "author": 1,    "meta": {        "location": "NYC",        "date": "never",        "event_url": "http: //google.com"    },    "featured_media": 1221}

WordPress doesn't allow you create resource directly. You need to authenticate your REST request. I am using the Basic Auth for authenticating WordPress REST API. You need to install a plugin. Grab it from here: https://github.com/WP-API/Basic-Auth

I have tested the following python code.

import base64import jsonimport requests;# Data to be senddata = {    "title": "test",    "content": "testingfrompython",    "status": "draft",    "author": 1,    "meta": {        "location": "NYC",        "date": "never",        "event_url": "http: //google.com"    },    "featured_media": 1221}# I am using basic auth plugin to for WP API authenticaitonusername = 'admin'password = 'blood9807'# Encode the username and password using base64creds = base64.b64encode(username + ':' + password)# Create headers to be sendheaders = {    'Authorization': 'Basic ' + creds,    'Content-type': 'application/json',     'Accept': 'text/plain'}# Convert the python dictionary to JSONdata_json = json.dumps(data)# Create a postr = requests.post('http://paathsala-plugin.test/wp-json/wp/v2/experience', data = data_json, headers = headers )print(r)

@Peter Foti can you try below function for add meta value in your API.

add_post_meta( <value>, <name>, $meta_value ,true );

For Reference see this Link