Select trable row with id notice: undefined variable: id in C:\wamp64server\www\register\approve\n.php on line 9

<?php 
session_start();
include("connectdb.php");
//include("statuselectricity.php");
 if( isset( $_POST['id'])) {
    $id = $_POST['id']; 
} 

          $query = "SELECT * from approvedelectricity  where id` = '$id';";
     $result= mysqli_query($conn, $query);
 if(mysqli_num_rows($result)>0){
                   while($row = mysqli_fetch_array($result))
    $rows[] = $row;
foreach($rows as $i){
            if($i['message']=='approved'){
                echo " liked your post";
}else{
                echo "rejected";
}
}
}
if (!$conn) {
    die("Connection failed: " . mysqli_connect_error());
}
echo "Connected successfully";
mysqli_close($conn);
?><br/><a href="index.php">BACK</a>