Prepared statement didn't execute - php

Question

I have simple web application with back end in PHP. I tried for three hours but couldn't solve the problem.
My code is as follows:
1. db_connect.php
<?php
define("HOST", '127.0.0.1');
define("USER", 'root');
define("PASSWORD", '');
define("DB", 'tourist guide');
$con = new mysqli(HOST,USER,PASSWORD,DB);
if ($con->connect_errno){
die("Database Connection Failed");
exit();
}
2. index.php
<?php
require_once 'db_connect.php';
$response = array();
$result = "";
if (isset($_POST['firstname']) && isset($_POST['lastname']) && isset($_POST['email'])&& isset($_POST['password'])) {
$firstname = $_POST['firstname'];
$lastname = $_POST['lastname'];
$email = $_POST['email'];
$password = $_POST['password'];
$stmt = $con->prepare("INSERT INTO
user_accounts
(first_name,last_name,email,password)
VALUES
(?,?,?,?)");
echo 'prepared statement executed. ';
$stmt->bind_param('ssss', $firstname, $lastname, $email, $password);
echo 'values given. ';
$result = $stmt->execute();
echo 'statement is executed. ';
$stmt->close();
}
if ($result) {
$response["success"] = 1;
$response["message"] = "account successfully created.";
echo json_encode($response);
} else {
$response["success"] = 0;
$response["message"] = "An error occurred during registration.";
echo json_encode($response);
}
?>
And the output is as follows:
prepared statement executed. values given. statement is executed. {"success":0,"message":"An error occurred during registration."}
Only the mistake must be $result = $stmt->execute();. Am I wrong here? or the error is something else? plz help.
UPDATE:
From fred's comment I added:
if(!$stmt->execute()){trigger_error("there was an error....".$con->error, E_USER_WARNING);}
Now he real error is showing:
Cannot add or update a child row: a foreign key constraint fails
looks like the error is in my database foreign keys...I'll solve it later..If you know about the error right now, then please say me...thanks fred.

Answer 1

As per OP's wish to close the question, seeing that the error has been found.
It seems like you're closing your DB connection too soon.
Place $stmt->close(); before your closing ?> tag.
Also, instead of the whole if/else block including $result = $stmt->execute(); replace it with if(!$stmt->execute()){trigger_error("There was an error....".$con->error, E_USER_WARNING);} in order to see the real error why it's failing.
You should also replace die("Database Connection Failed"); with
die('Connection failed [' . $con->connect_error . ']');
to get the real error in case your connection should ever fail.
Seeing that the problem is with your foreign keys.