Prevent customers from certain zipcodes from checking out

validate_zipcodes.php

<?php
function pr_validate_zipcodes( $fields, $errors ) {
	// Enter your zip codes in this array
	$excluded_zips = array( '12345', '23456' );
	if( in_array( $fields['shipping_postcode'], $excluded_zips ) ) {
		$errors->add( 'validation', 'That zipcode is not allowed' );
	}
}
add_action( 'woocommerce_after_checkout_validation', 'pr_validate_zipcodes', 10, 2 );