Hi,
This code should work for the order creation notification and the order admin notification:
<?php
if(!empty($data->order_discount_code)){ ?>
<p>
<span style="color:#1c8faf !important;font-weight:bold;">COUPON used :</span> {VAR:order.order_discount_code}
</p>
<?php
}
?>
This should work for the order status notification and the payment notification emails:
<?php
if(!empty($data->cart->order_discount_code)){ ?>
<p>
<span style="color:#1c8faf !important;font-weight:bold;">COUPON used :</span> {VAR:order.order_discount_code}
</p>
<?php
}
?>
The second code might also work for the order creation notification and the order admin notification but it would require some testing to verify that.