Remove VAT if specific post code entered

add_action( 'woocommerce_checkout_update_order_review', 'taxexempt_checkout' );

function taxexempt_checkout( $post_data ) {
        global $woocommerce;
        $woocommerce->customer->set_is_vat_exempt( false );
        parse_str($post_data);
        if ( $billing_postcode == '32444' ) $woocommerce->customer->set_is_vat_exempt( true );
}