To remove free gift row from email and frontend order detail section - Smart Coupons For WooCommerce Coupons by WebToffee (https://wordpress.org/plugins/wt-smart-coupons-for-woocommerce/)

functions.php

<?php // do not copy this line
add_filter('woocommerce_get_order_item_totals', 'wt_sc_remove_free_gift_row', 12, 3);
function wt_sc_remove_free_gift_row($total_rows, $order, $tax_display)
{
	$out = array();
	foreach($total_rows as $row_key => $row_value)
	{
		if(false === strpos($row_key, 'free_product_'))
		{
			$out[$row_key] = $row_value;
		}
	}

	return $out;
}