Example of cross posting from a WordPress subsite to the parent site

pacc_cross_post.php

<?php
/*
Plugin Name: PACC Cross Post
Plugin URI: http://thepacc.com
Description: Allows subsites to cross post to the main site
Author: Topher
Version: 1.0
Author URI: http://codeventure.net
*/

/**
 * Allows subsites to cross post to the main site
 *
 * @package PACC_Cross_Post
 * @since PACC_Cross_Post 1.0
 * @author Topher
 */

/**
 * Instantiate the PACC_Cross_Post instance
 * @since PACC_Cross_Post 1.0
 */
add_action( 'plugins_loaded', array( 'PACC_Cross_Post', 'instance' ) );

/**
 * Main Cross Post Class
 *
 * Contains the main functions for the admin side of Cross Post
 *
 * @class PACC_Cross_Post
 * @version 1.0.0
 * @since 1.0
 * @package PACC_Cross_Post
 * @author Topher
 */
class PACC_Cross_Post {

	/**
	* Instance handle
	*
	* @static
	* @since 1.2
	* @var string
	*/
	private static $__instance = null;

	/**
	 * PACC_Cross_Post Constructor, actually contains nothing
	 *
	 * @access public
	 * @return void
	 */
	private function __construct() {}

	/**
	 * Instance initiator, runs setup etc.
	 *
	 * @access public
	 * @return self
	 */
	public static function instance() {
		if ( ! is_a( self::$__instance, __CLASS__ ) ) {
			self::$__instance = new self;
			self::$__instance->setup();
		}

		return self::$__instance;
	}

	/**
	 * Runs things that would normally be in __construct
	 *
	 * @access private
	 * @return void
	 */
	private function setup() {

		// only do this in the admin area
		if ( is_admin() ) {
			add_action( 'save_post', array( $this, 'save' ) );
			add_action( 'add_meta_boxes', array( $this, 'menu_meta_box' ) );
		}
	}

	/**
	 * Make meta box holding select menu of Menus
	 *
	 * @access public
	 * @return void
	 */
	public function menu_meta_box( $post_type ) {

		// limit meta box to certain post types
		$post_types = array( 'articles' );

		if ( in_array( $post_type, $post_types ) ) {
			add_meta_box(
				'wp-fetaured-menu',
				esc_html__( 'Cross Post', 'thepacc' ),
				array( $this, 'render_menu_meta_box_contents' ),
				$post_type,
				'side',
				'high'
			);
		}
	}

	/**
	 * Render select box of WP Menus
	 *
	 * @access public
	 * @return void
	 */
	public function render_menu_meta_box_contents() {

		global $post;

		// Add an nonce field so we can check for it later.
		wp_nonce_field( 'thepacc', 'cross_post_nonce' );

		// Use get_post_meta to retrieve an existing value from the database.
		$cross_post_value = get_post_meta( $post->ID, '_cross_post_value', true );

		// Display the form, using the current value.

		// only show the checkbox if this post has NOT been pushed to the front
		//if ( 1 != absint( $cross_post_value ) ) {
		if ( 1 ) {
			echo '<p>';
			esc_html_e( 'Would you like to request that this post appear on the main PACC site? ', 'thepacc' );
			echo '</p>';

			echo '<input type="checkbox" name="_cross_post_value" id="_cross_post_value" value="1"' . checked( $cross_post_value, 1, false ) . '/>' . "\n";
			echo '<label for="_cross_post_value">' . __( 'Yes', 'thepacc' ) . '</label>' . "\n";
		} else {
			echo '<p>This Article has already been published to the main PACC site.</p>' . "\n";
		}

	}

	/**
	 * Updates the options table with the form data
	 *
	 * @access public
	 * @param int $post_id
	 * @return void
	 */
	public function save( $post_id ) {

		// Check if the current user is authorised to do this action.
		$post_type = get_post_type_object( get_post( $post_id )->post_type );
		if ( ! current_user_can( $post_type->cap->edit_post, $post_id ) ) {
			return;
		}

		// Check if our nonce is set.
		if ( ! isset( $_POST['cross_post_nonce'] ) ) {
			return;
		}

		// Verify that the nonce is valid.
		if ( ! wp_verify_nonce( $_POST['cross_post_nonce'], 'thepacc' ) ) {
			return;
		}

		// don't run on autosave
		if ( defined( 'DOING_AUTOSAVE' ) && DOING_AUTOSAVE ) {
			return $post_id;
		}

		// Don't save revisions
		if ( is_int( wp_is_post_revision( $post_id ) ) ) {
			return $post_id;
		}

		// Sanitize the user input.
		$cross_post_value = sanitize_text_field( $_POST['_cross_post_value'] );

		// Update the meta field.
		update_post_meta( $post_id, '_cross_post_value', absint( $cross_post_value ) );

		if ( 1 == absint( $cross_post_value ) && $_POST['original_publish'] == 'Publish' ) { // This doesn't work if the site is not English, e.g. Publish might be Pubblica
 
			// get the original post
			$post = get_post( $post_id, 'ARRAY_A' );

			$terms = $_POST[ 'post_category' ];

			// get the term names in an array
			foreach ( $terms as $key => $term_id ) {
				$term = get_term( absint( $term_id ), 'category' );
				if ( $term && ! is_wp_error( $term ) ) {
					$term_names[] = $term->name;
				}
			}

			// We need to add a parent category
			$term_names[] = 'Article';

			// reset some post data
			$post['post_type']   = 'post';
			$post['post_status'] = 'pending';
			$post['ID'] = '';

			// get some info about the current post for feeding into meta on the cross post
			$site_url = get_site_url();
			$post_url = $site_url . '/' . $_POST['post_type'] . '/' . $post['post_name'] . '/';
			$blog_id = get_current_blog_id();

			// switch to the main blog for posting
			switch_to_blog( 1 );

				// get the term names in an array
				foreach ( $term_names as $key => $term_name ) {
					wp_create_category( wp_kses_post( $term_name ) );
				}

				// remove the save action to avoid a loop
				remove_action( 'save_post', array( $this, 'save' ) );

				// make the cross post
				$new_post_id = wp_insert_post( $post );

				// add meta data to the cross post
				add_post_meta( $new_post_id, 'cross_posted', absint( $cross_post_value ), true );
				add_post_meta( $new_post_id, 'remote_url', esc_url( $post_url ), true );
				add_post_meta( $new_post_id, 'source_site_id', absint( $blog_id ), true );

				// send the categories with the cross post
				$set_terms = wp_set_object_terms( $new_post_id, $term_names, 'category' );

			// go back to the original blog
			restore_current_blog();

		}
	}
}
?>