Prevent shipping to PO box addresses in WooCommerce

gistfile1.txt

/**
 * Prevent shipping to PO box addresses in WooCommerce
 */
add_action('woocommerce_after_checkout_validation', 'deny_pobox_postcode');

function deny_pobox_postcode($posted) {
    // Determine if we are checking the shipping or billing address
    $address  = isset($posted['shipping_address_1']) ? $posted['shipping_address_1'] : $posted['billing_address_1'];
    $postcode = isset($posted['shipping_postcode']) ? $posted['shipping_postcode'] : $posted['billing_postcode'];

    // Characters to replace
    $replace  = array(' ', '.', ',');

    // Clean and normalize the address and postcode
    $address  = strtolower(str_replace($replace, '', $address));
    $postcode = strtolower(str_replace($replace, '', $postcode));

    // Check if the address or postcode contains 'pobox'
    if (strpos($address, 'pobox') !== false || strpos($postcode, 'pobox') !== false) {
        wc_add_notice(__('Sorry, we cannot ship to PO BOX addresses.', 'woocommerce'), 'error');
    }
}