add woocommerce admin order vat and ssn fields

gistfile1.php

// Add VAT and SSN fields in billing address display
add_filter( 'woocommerce_order_formatted_billing_address', 'custom_add_vat_ssn_formatted_billing_address', 10, 2 );
function custom_add_vat_ssn_formatted_billing_address( $fields, $order ) {
	$fields['vat'] = $order->billing_vat;
	$fields['ssn'] = $order->billing_ssn;

	return $fields;
}

add_filter( 'woocommerce_admin_billing_fields', 'custom_admin_billing_fields' );
function custom_admin_billing_fields( $fields ) {
	$fields['vat'] = array(
		'label' => __( 'VAT', 'your-domain' ),
		'show'  => true
	);

	$fields['ssn'] = array(
		'label' => __( 'SSN', 'your-domain' ),
		'show'  => true
	);

	return $fields;
}