How do I update the unit price of an order item on Add to Cart in Commerce 2.x?
I managed to update the price by updating the order item of order rather than the order item in event.

$items = $event-&gt;getOrder()-&gt;getItems();
foreach ($items as $key =&gt; $item) {
    $currencyCode = $item-&gt;getUnitPrice()-&gt;getCurrencyCode();
    $unit_price = new Price('20.00', $currencyCode);
    $item-&gt;setUnitPrice($unit_price,TRUE);
    $item-&gt;save();
}