Require a user meta field to access a category of posts with Paid Memberships Pro

hide_conference_posts2.php

/*
	Require conference user meta to view conference category posts.
	
  Custom field is added via PMPro Register Helper Below.
  
  Add all of this code to your active theme's functions.php or a custom plugin.
*/
add_filter("pmpro_has_membership_access_filter", "hide_conference_posts2", 10, 4);
function hide_conference_posts2($hasaccess, $thepost, $theuser, $post_membership_levels)
{
	global $wpdb;
		
	//if PMPro says false already, return false
	if(!$hasaccess)
		return false;
		
	//if the post is in the conference category and the user has not purchased the conference addon package package, then block
	if(has_category('conference', $thepost))
	{	
		//make sure they purchased the addon package
		$conference = get_user_meta($theuser->ID, "conference", true);
		if(empty($conference))
			$hasaccess = false;
	}
	
	return $hasaccess;
}

//add conference field
function my_pmprorh_init()
{
    //don't break if Register Helper is not loaded
    if(!function_exists("pmprorh_add_registration_field"))
    {
        return false;
    }
    	
    $fields[] = new PMProRH_Field(
        "conference",                   // input name, will also be used as meta key
        "checkbox",                   // type of field
        array(
            "text"=>"I want to attend the annual conference. ($300/year)",
			"memberslistcsv"=>true,
			"profile"=>"admin_only",
        ));
    //add the fields into a new checkout_boxes are of the checkout page
    foreach($fields as $field)
        pmprorh_add_registration_field(
            "checkout_boxes", // location on checkout page
            $field            // PMProRH_Field object
        );
    //that's it. see the PMPro Register Helper readme for more information and examples.
}
add_action("init", "my_pmprorh_init");