I also got the same issue, First of all need to know either it works with sending the GET request to defined URL in Service dashboard.
if it works then there would be a problem with our code , if it doesn't work with sandbox mode, then there is only one way to make it live and then test.
Here is my code I am using for testing and inserting some records into db just to test if fortumo touch this page or not .
$servername = "servername";
$username = "username";
$password = "password";
$dbname = "dbname";
// Create connection
$conn = new mysqli($servername, $username, $password, $dbname);
// Check connection
if ($conn->connect_error) {
die("Connection failed: " . $conn->connect_error);
}
$sql = "INSERT INTO wpcf_terms (name, slug)
VALUES ('John', 'john@example.com')";
if(isset($_GET['credit_name'])) {
if ($conn->query($sql) === TRUE) {
echo "New record created successfully";
} else {
echo "Error: " . $sql . "<br>" . $conn->error;
}
}
$conn->close();