is_vat_exempt is not working

Hello, small problem, I have an option during check were the customer can select vat exemption.
When clicked the customer is vat exempt.
I use
$customer->set_is_vat_exempt( true );
and
update_post_meta($order_id, '_is_vat_exempt','yes');
But EU VAT Compliance Assistant for WooCommerce will keep calculating vat
IS there a different meta I need to use to get it working?
Thank you
Jean Paul