<?php
$servername = "localhost";
$username = "root";
$password = "pass";
$dbname = "db";

// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
     die("Connection failed: " . $conn->connect_error);
}

$sql = "SELECT timestamp_activated, timestamp_expire FROM user_subscriptions WHERE id = :id LIMIT 1";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
     // output data of each row
     while($row = $result->fetch_assoc()) {
$datetime1 = new DateTime('. $row["timestamp_activated"]. ');
$datetime2 = new DateTime('. $row["timestamp_expire"]. ');
$interval = $datetime1->diff($datetime2);
echo $interval->format('%a');

     }
} else {
     echo "0 results";
}

$conn->close();
?>

SELECT TIMESTAMPDIFF(DAY, timestamp_activated, timestamp_expire) AS daysRemaining
FROM user_subscriptions
WHERE id = :id
LIMIT 1