Stop and prevent members from checking out for a membership level they are already a member of.

pmpro-block-checkout-if-has-membership-level.php

<?php
/**
 * Prevent users from checking out for a specific set of levels if they already have that level.
 *
 * Set the $blocked_levels array to the level ids you want to block in each function.
 *
 * You can add this recipe to your site by creating a custom plugin
 * or using the Code Snippets plugin available for free in the WordPress repository.
 * Read this companion article for step-by-step directions on either method.
 * https://www.paidmembershipspro.com/create-a-plugin-for-pmpro-customizations/
 */

// Warn the user on the  checkout page if they already have a membership level in the checkout levels.
function my_pmpro_checkout_set_message_has_level() {
	global $current_user, $pmpro_level, $pmpro_checkout_level_ids, $pmpro_msg, $pmpro_msgt;

	// Add the level ids to stop registration for here.
	$blocked_levels = array( 1, 2, 3 );

	// bail if necessary.
	if ( ! is_user_logged_in() || ! pmpro_hasMembershipLevel( $blocked_levels ) || ! empty( $pmpro_msg ) ) {
		return;
	}

	$checkout_levels = array();

	// get the checkout levels
	if ( ! empty( $pmpro_checkout_level_ids ) ) {
		$checkout_levels = $pmpro_checkout_level_ids;
	} elseif ( ! empty( $pmpro_level ) ) {
		$checkout_levels = array( $pmpro_level->id );
	}

	// get all membership level ids for user
	$user_levels    = pmpro_getMembershipLevelsForUser( $current_user->ID );
	$user_level_ids = array();
	foreach ( $user_levels as $user_level ) {
		$user_level_ids[] = $user_level->id;
	}

	// get the checkout level ids matching the user's membership level ids
	$has_levels = array_intersect( $user_level_ids, $checkout_levels );

	// get the has levels matching the blocked levels
	$has_levels = array_intersect( $has_levels, $blocked_levels );

	// bail if user does not have a membership level in the checkout levels
	if ( empty( $has_levels ) ) {
		return;
	}

	// Let's let the user know they already have the level.
	if ( empty( $pmpro_msg ) ) {
		foreach ( $has_levels as $has_level ) {
			// get the array key for the user_levels where have level matches the object->id
			$key   = array_search( $has_level, array_column( $user_levels, 'id' ) );
			$level = $user_levels[ $key ];

			// Set the message.
			/* translators: %s: membership level name */
			$alert_message = sprintf( __( 'You are already a member of the <strong>%s</strong> membership level.', 'paid-memberships-pro' ), $level->name );
			pmpro_setMessage( $alert_message, 'pmpro_error' );
			break;
		}
	}
}
add_action( 'pmpro_checkout_after_parameters_set', 'my_pmpro_checkout_set_message_has_level' );

// Block users from registering for the same level they already have, unless the level is expiring soon and the user can renew.
function my_pmpro_same_level_registration_checks( $okay ) {
	global $pmpro_level;

	// Add the level ids to stop registration for here.
	$blocked_levels = array( 1, 2, 3 );

	// bail if things are not okay
	if ( ! $okay || ! is_user_logged_in() ) {
		return $okay;
	}

	$level_id = $pmpro_level->id;

	// check if level id is in blocked levels and if user already have a blocked membership level set message.
	if ( in_array( $level_id, $blocked_levels ) && pmpro_hasMembershipLevel( $level_id ) ) {
		pmpro_setMessage( 'You already have this membership level.', 'pmpro_error' );
		$okay = false;
	}

	return $okay;
}
add_action( 'pmpro_registration_checks', 'my_pmpro_same_level_registration_checks' );

// Remove all member action links for specific levels.
function my_pmpro_remove_member_action_links_levels( $pmpro_member_action_links, $level_id ) {

	// Add the level ids to remove action links for here:
	$blocked_levels = array( 1, 2, 3 );

	if ( in_array( $level_id, $blocked_levels ) ) {
		$pmpro_member_action_links = array();
	}

	return $pmpro_member_action_links;
}
add_filter( 'pmpro_member_action_links', 'my_pmpro_remove_member_action_links_levels', 10, 2 );