PHP: No output from $row variable even if it is already defined - php

Question

I don't know why it doesn't show up anything, I already tested my query and it is working in my phpmyadmin, but in my php code it does not work upon adding the AS keyword. My goal for this is to place a value to a variable coming from the SUM() keyword.
<?php
require_once "user-connect.php";
$user = $_SESSION['id'];
$sql = "SELECT SUM(total) AS sumz FROM cart WHERE userID = $user AND month(orderDate) = month(now()) AND day(orderDate) = day(now())";
$result = $link->query($sql);
if ($result->num_rows > 0) {
$row = $result->fetch_assoc();
echo $row['sumz'];
}
if (mysqli_query($link, $sql)) {
} else {
echo "Error: " . $sql . "" . mysqli_error($link);
} ?>
<table cellspacing="0">
<tbody>
<tr class="cart-subtotal">
<th>Cart Subtotal</th>
<td><span class="amount"><?php echo $row['sumz']; ?></span></td>
</tr>

Answer 1

You can use:
$sql = "SELECT SUM(total) FROM cart WHERE..."
And in HTML:
<td><span class="amount"><?php echo $row['SUM(total)']; ?></span></td>

Answer 2

Take a look at PHP fetch assoc guide.
while ($row = $result->fetch_assoc()) {
echo $row['sumz'];
}
An example of getting the SUM value
<?php
$sql="SELECT sum(amount) as total FROM table";
$result = mysqli_query($sql);
while ($row = mysqli_fetch_assoc($result)) {
echo $row['total'];
}
mysqli_close($con);
?>