Woocommerce: Hide specified shipping options when shipping to PO boxes

functions.php

<?php 
// Paste everything below this line to your theme's functions.php file.

add_filter('woocommerce_package_rates', function($rates, $package) {

    $destination = $package['destination'];

    // Put postcode, address 1 and address 2 into an array
    $check_address = array(
        $destination['address'],
        $destination['address_2'],
        $destination['postcode'],
    );

    // Implode address, make lowercase, and remove spaces and full stops
    $check_address = strtolower(str_replace(array(' ', '.'), '', implode('-', $check_address)));

    // Check for po boxes in the combined address string
    if (strstr($check_address, 'pobox')) {

        // Hide shipping options not suitable for po boxes
        foreach ($rates as $rate_id => $rate) {
            if (preg_match('/fastway|couriers please safe drop|couriers please no safe drop/i', $rate->label)) {
                unset($rates[$rate_id]);
            }
        }
    }

    return $rates;
}, 100, 2);