[WooCommerce Shipping Multiple Addresses] Adding additional fields to addresses

wc-shipping-multiple-addresses-additional-address-fields.php

function custom_shipping_fields( $fields, $country ) {
    $fields['shipping_test'] = array(
        'label' => 'Test',
        'placeholder'   => 'Test'
    );
    return $fields;
}
add_filter( 'woocommerce_shipping_fields', 'custom_shipping_fields', 10, 2 );

function display_custom_shipping_fields( $formatted_address, $address ) {
    if ( isset( $address['shipping_test'] ) ) {
        $formatted_address .= '<br/>Test: '. $address['shipping_test'];
    }
    return $formatted_address;
}
add_filter( 'wc_ms_formatted_address', 'display_custom_shipping_fields', 10, 2 );

Add this filter to display the custom address fields in User >> Profile page.

add_filter( 'woocommerce_wcms_shipping_fields', 'custom_shipping_fields', 10, 2 );