How to use the WooCommerce Postcode Validator | https://www.ibenic.com/woocommerce-postcode-validator

field.php

<?php

/**
 * Shipping method id: rp_table_rate
 * You can use any ID here and replace rp_table_rate to add this field to your shipping method settings page.
 */
add_filter( 'woocommerce_settings_api_form_fields_rp_table_rate', 'ibenic_add_postcodes_field_a_shipping_method' );

/**
 * Add Postcodes field to the Table Rate
 *
 * @param array $fields
 *
 * @return mixed
 */
function ibenic_add_postcodes_field_a_shipping_method( $fields ) {
  // Unset it so that we can set it back and have it at the last place.
	unset( $fields['domestic_shipping_table']);

  // Adding postcodes field
	$fields['postcodes'] = array(
		'title'       => __( 'ZIP Codes', 'ibenic-table-rates' ),
		'type'        => 'textarea',
		'class'       => 'widefat',
		'css'         => 'width: 450px;',
		'default'     => '',
		'description' => sprintf( __( 'Postcodes containing wildcards (e.g. CB23*) or fully numeric ranges (e.g. <code>90210...99000</code>) are also supported. Please see the shipping zones <a href="%s" target="_blank">documentation</a>) for more information.', 'woocommerce' ), 'https://docs.woocommerce.com/document/setting-up-shipping-zones/#section-3' ),
	);

	$fields['domestic_shipping_table'] = array(
		'type'      => 'shipping_table'
	);

	return $fields;
}

validate.php

<?php

/**
 * Shipping method id: rp_table_rate
 * You can use any ID here and replace rp_table_rate to add this field to your shipping method settings page.
 */
add_filter( 'woocommerce_shipping_rp_table_rate_is_available', 'ibenic_is_shipping_method_available', 20, 3 );

/**
 * Check if the Table Rate is available or not.
 *
 * @param $available
 * @param $package
 * @param WC_Shipping_Method $method
 */
function ibenic_is_shipping_method_available( $available, $package, $method ) {
	if ( ! $available ) {
		return $available;
	}

	$compare_codes = $method->get_option( 'postcodes', '' );

	if ( ! $compare_codes ) {
		return $available;
	}


	$postcodes = array_filter( array_map( 'strtoupper', array_map( 'wc_clean', explode( "\n", $compare_codes ) ) ) );
	if ( ! $postcodes ) {
		return $available;
	}

	$shipping_code = $package['destination']['postcode'];
	$country       = $package['destination']['country'];
	$objects       = array();

  // Building our own objects
	foreach ( $postcodes as $index => $postcode ) {
		$object = new stdClass();
		$object->id = $index;
		$object->postcode = $postcode;
		$objects[] = $object;
	}

	$matches = wc_postcode_location_matcher( $shipping_code, $objects, 'id', 'postcode', $country );
  
  // We did not find any matching postcodes? Return it as not available.
	if ( ! $matches ) {
		return false;
	}

	return true;
}

validator.php

<?php

/**
 * Used by shipping zones and taxes to compare a given $postcode to stored
 * postcodes to find matches for numerical ranges, and wildcards.
 *
 * @since 2.6.0
 * @param string $postcode           Postcode you want to match against stored postcodes.
 * @param array  $objects            Array of postcode objects from Database.
 * @param string $object_id_key      DB column name for the ID.
 * @param string $object_compare_key DB column name for the value.
 * @param string $country            Country from which this postcode belongs. Allows for formatting.
 * @return array Array of matching object ID and matching values.
 */
function wc_postcode_location_matcher( $postcode, $objects, $object_id_key, $object_compare_key, $country = '' ) {
	$postcode           = wc_normalize_postcode( $postcode );
	$wildcard_postcodes = array_map( 'wc_clean', wc_get_wildcard_postcodes( $postcode, $country ) );
	$matches            = array();

	foreach ( $objects as $object ) {
		$object_id       = $object->$object_id_key;
		$compare_against = $object->$object_compare_key;

		// Handle postcodes containing ranges.
		if ( strstr( $compare_against, '...' ) ) {
			$range = array_map( 'trim', explode( '...', $compare_against ) );

			if ( 2 !== count( $range ) ) {
				continue;
			}

			list( $min, $max ) = $range;

			// If the postcode is non-numeric, make it numeric.
			if ( ! is_numeric( $min ) || ! is_numeric( $max ) ) {
				$compare = wc_make_numeric_postcode( $postcode );
				$min     = str_pad( wc_make_numeric_postcode( $min ), strlen( $compare ), '0' );
				$max     = str_pad( wc_make_numeric_postcode( $max ), strlen( $compare ), '0' );
			} else {
				$compare = $postcode;
			}

			if ( $compare >= $min && $compare <= $max ) {
				$matches[ $object_id ]   = isset( $matches[ $object_id ] ) ? $matches[ $object_id ] : array();
				$matches[ $object_id ][] = $compare_against;
			}
		} elseif ( in_array( $compare_against, $wildcard_postcodes, true ) ) {
			// Wildcard and standard comparison.
			$matches[ $object_id ]   = isset( $matches[ $object_id ] ) ? $matches[ $object_id ] : array();
			$matches[ $object_id ][] = $compare_against;
		}
	}

	return $matches;
}

wc-zones.php

<?php

// Postcode range and wildcard matching.
  $postcode_locations = $wpdb->get_results( "SELECT zone_id, location_code FROM {$wpdb->prefix}woocommerce_shipping_zone_locations WHERE location_type = 'postcode';" );

  if ( $postcode_locations ) {
    $zone_ids_with_postcode_rules = array_map( 'absint', wp_list_pluck( $postcode_locations, 'zone_id' ) );
    $matches                      = wc_postcode_location_matcher( $postcode, $postcode_locations, 'zone_id', 'location_code', $country );
    $do_not_match                 = array_unique( array_diff( $zone_ids_with_postcode_rules, array_keys( $matches ) ) );

    if ( ! empty( $do_not_match ) ) {
      $criteria[] = 'AND zones.zone_id NOT IN (' . implode( ',', $do_not_match ) . ')';
    }
  }