Load OptinMonster Opt-ins based on the post tag.

optin-monster-load-on-tag.php

<?php
/*
 * Plugin Name: OptinMonster Load on Tag
 * Plugin URI:  https://gist.github.com/BFTrick/bc0dab3881660645aaf6
 * Description: Load OptinMonster Opt-ins based on the post tag.
 * Author: Patrick Rauland
 * Author URI:  http://speakinginbytes.com
 * Version: 1.0
 */

if ( ! defined( 'ABSPATH' ) ) exit; // Exit if accessed directly


class Optin_Monster_Load_On_Tag {

	/**
	 * Constructor
	 */
	public function __construct() {
		add_filter( 'the_content', array( $this, 'load_on_tag' ), 999 );
	}

	/**
	 * Load the optin based on if a tag is present
	 *
	 * @since  1.0
	 * @param  $content the content of the post
	 * @return string
	 */
	public function load_on_tag( $content) {

		// enter the tag you wish to target
		$target_tag = array( 'woocommerce' );

		// enter the optin slug. You can find this in the WordPress admin after clicking on OptinMonster in the menu to see a list of opt-ins. Then look for the 'Slug' column of the opt-in you wish to include
		$optin_id   = 'qiyzpkho8s-post';

		// only load on single post pages
		if ( is_single() ) {
			// only load the optin on a post that has the target tag
			if ( has_tag( $target_tag ) ) {
				// display the optin
				$content .= optin_monster_tag( $optin_id, true );
			}
		}

		return $content;
	}

}

// load after optin_monster has loaded
add_filter( 'optin_monster_init', 'load_optin_monster_load_on_tag' );
function load_optin_monster_load_on_tag() {
	// make sure the function to generate the optin exists
	if ( function_exists( 'optin_monster_tag' ) ) {
		return new Optin_Monster_Load_On_Tag();
	}
}