Notice Undefined index:

Question

<?php 
 <form id="formOftd" method= "POST" >
 $i = 1;
        if ($result = $mysqli->query($query)) {
            while ($row = $result->fetch_assoc()) {
                $count = $row["count"];
                $price = floor($row["currency"]*$row["buyPrice"]);
                $iid = $row["iid"];
                echo '
                <td id="dist_td'.$i.'"><input type="hidden" name="dist_'.$iid.'" id="dist_'.$i.'" value="-" ></td>
                <td><button type="button" class="btn btn-success" onclick="mysavesale('.$iid.')">'.$lb_save.'</button>';
                
        }
     $result->free();
    }
    $mysqli->close();
</form>


$distribution = $_POST['dist_48'];
echo $distribution;     
?>

After echo $distribution I have error: Undefined index: dist_48. $iid is from Database and 4is already exists