Only let certain members post BuddyPress activity when using PMPro and PMPro BuddyPress.

my_bp_activity_filter.php

/**
 * Only let certain members post BuddyPress activity.
 * This code works with BuddyPress and BuddyBoss.
 * This code only filters the main activity page.
 * Posting to groups you are a member of still works.
 *
 * Make sure BuddyPress (or BuddyBoss), PMPro, and PMPro BuddyPress are all active.
 * Copy this code into a custom plugin or Code Snippet.
 */

// Define the levels that CAN post activity here.
define( 'MY_LEVELS_WITH_ACTIVITY', array(1,4,5) );
 
// JS to disable the activity form and show error
function my_hide_bp_activity_form() {
	// Bail if no PMPro or the current user is a paying member
	if ( ! function_exists( 'pmpro_hasMembershipLevel' ) || pmpro_hasMembershipLevel( MY_LEVELS_WITH_ACTIVITY ) ) {
		return;
	}
	// Bail if we're on a group page.
	if ( bp_is_group() ) {
		return;
	}
	
	// Change the text here. Add a link to your levels page.
?>
<script>
jQuery(document).ready(function() {
	jQuery('#whats-new-textarea').html('<p>You must have a paying membership to post activity.</p>');
});
</script>
<?php
}
add_action( 'bp_after_activity_post_form', 'my_hide_bp_activity_form' );

// Filter to stop activity from posting.
function my_bp_activity_filter( $activity ) {
	if ( ! function_exists( 'pmpro_hasMembershipLevel' ) ) {
		return $activity;
		
	}
	if ( $activity->component == 'activity' && ! pmpro_hasMembershipLevel( MY_LEVELS_WITH_ACTIVITY ) ) {
		$activity->error_type = 'wp_error';
		$activity->errors->add( 'pmpro_bp_membership_required', 'Only certain members may post activity.' );
	}
	
	return $activity;
}
add_filter( 'bp_activity_before_save', 'my_bp_activity_filter' );