How to add customer capability after Woocommerce purchase?

patrick

Is it possible to add a capability after someone purchases a product in my child's function file? Tried this but did not worked

add_action( 'cap_added', 'change_user_cap_with_purchase', 1 ); 
function change_user_cap_with_purchase ( $order_id ){
            $order = wc_get_order( $order_id );

            foreach( $order->get_items() as $item ) {
                // Product ID
                if ( $item['product_id'] == 999 ) {
                function add_cap_to_role() {
    $customer = get_role('customer');
    $customer->add_cap('cst11');
 }
            }        
}