The following snippet would add a message to the cart if a certain coupon is not applied. Replace ‘coupon_code’ by the actual coupon code and change the message to your needs…
add_action( 'woocommerce_after_cart_table', function() {
if ( WC()->cart->has_discount( 'coupon_code' ) ) return;
?>
<div class="soft79-notice clearfix">
<p>Spend $ 60 to get a <strong>free gift</strong>!</p>
</div>
<?php
}, 5 );
Place it in your child theme’s functions.php.