Require an addon package for access to a post category with Paid Memberships Pro and PMPro Addon Packages.

hide_conference_posts.php

/*
  Require an addon package for access to a post category.
	
  Be sure to change the value of the addon package ID variable below.
  
  Add all of this code to your active theme's functions.php or a custom plugin.
*/

//require a specific addon package to access posts in the conference category
add_filter("pmpro_has_membership_access_filter", "hide_conference_posts", 10, 4);
function hide_conference_posts($hasaccess, $thepost, $theuser, $post_membership_levels) {
	global $wpdb;
	
	//UPDATE THIS to the post ID of your addon package
	$addon_package_post_id = 627;

	//if PMPro Addon Packages is not installed, return
	if(!function_exists('pmproap_hasAccess'))
	  return $hasaccess;
		
	//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', $thepost)) {	
		//make sure they purchased the addon package
		if(!pmproap_hasAccess($addon_package_post_id, $theuser->ID))
			$hasaccess = false;
	}
	
	return $hasaccess;
}

//show a link to checkout for the addon package on posts in the conference category
add_filter("pmpro_non_member_text_filter", "pmproap_pmpro_text_filter_for_conference_posts", 15);
add_filter("pmpro_not_logged_in_text_filter", "pmproap_pmpro_text_filter_for_conference_posts", 15);
function pmproap_pmpro_text_filter_for_conference_posts($text) {
	global $wpdb, $current_user, $post, $pmpro_currency_symbol;

	//UPDATE THIS to the post ID of your addon package
	$addon_package_post_id = 627;

	if(!empty($post)) {
		if(has_category('conference', $post) && !pmproap_hasAccess($current_user->ID, $addon_package_post_id)) {
			//which level to use for checkout link?
			$text_level_id = pmproap_getLevelIDForCheckoutLink($addon_package_post_id, $current_user->ID);
			
			//what's the price
			$pmproap_price = get_post_meta($addon_package_post_id, "_pmproap_price", true);

			//check for all access levels
			$all_access_levels = apply_filters("pmproap_all_access_levels", array(), $current_user->ID, $addon_package_post_id);	
			
			//update text
			if(!empty($all_access_levels)) {
				$level_names = array();
				foreach ($all_access_levels as $level_id) {
					$level = pmpro_getLevel($level_id);
					$level_names[] = $level->name;
				}
				
				$text = "<p>This content requires that you purchase additional access. The price is " . $pmpro_currency_symbol . $pmproap_price . " or free for our " . pmpro_implodeToEnglish($level_names) . " members.</p>";
				$text .= "<p><a href=\"" . pmpro_url("checkout", "?level=" . $text_level_id . "&ap=" . $addon_package_post_id) . "\">Purchase this Content (" . pmpro_formatPrice($pmproap_price) . ")</a> <a href=\"" . pmpro_url("levels") . "\">Choose a Membership Level</a></p>";
			} else {				
				$text = "<p>This content requires that you purchase additional access. The price is " . pmpro_formatPrice($pmproap_price) . ".</p>";
				$text .= "<p><a href=\"" . pmpro_url("checkout", "?level=" . $text_level_id . "&ap=" . $addon_package_post_id) . "\">Click here to checkout</a></p>";
			}
		}
	}	

	return $text;
}

This recipe is included in the blog post on "Sell Access to a Single Post Category Using the Addon Packages Plugin" at Paid Memberships Pro here: https://www.paidmembershipspro.com/sell-access-single-post-category-using-addon-packages-plugin/