<?php

if(isset($_GET['email']) && isset($_GET['hash'])) {

    include_once('php_includes/connect.php');
    //verify
    $email = mysqli_real_escape_string($_GET['email']); //set email variable
    $hash = mysqli_real_escape_string($_GET['hash']); //set hash variable

    $sql = "SELECT email, hash, activated FROM `users` WHERE email = '$email' AND hash = '$hash' AND activated = '0' LIMIT 1" or die(mysqli_error());

    $result = mysqli_query($connection, $sql);

    if($result) {
        $sql = "UPDATE `users` SET activated='1' WHERE email='$email' AND hash='$hash' AND activated = '1' LIMIT 1" or die(mysqli_error());
        header("location: message.php?msg="); //PAGE WITH LINK TO LOGIN
        exit();

    } else {
        echo '<div class="statusmsg">The url is either invalid or you already have activated your account.</div>';
    }
} else {
    echo '<div class="statusmsg">Invalid approach. Please use the link that has been sent to your email.</div>';
}

<?php

if(isset($_GET['email']) && isset($_GET['hash'])) {

    include_once('php_includes/connect.php');
    //verify
    $email = mysqli_real_escape_string($_GET['email']); //set email variable
    $hash = mysqli_real_escape_string($_GET['hash']); //set hash variable
    $activated = 1;
    $not_activated = 0;

    $sql = $connection->prepare("SELECT email, hash, activated FROM `users` WHERE email=? AND hash=? AND activated=? LIMIT 1") or die(mysqli_error());
    $sql->bind_param("ssi", $email, $hash, $not_activated);
    $result = $sql->execute();
    $sql->execute();

    if($result) {

        $sql = $connection->prepare("UPDATE `users` SET activated=? WHERE email=? AND hash=? AND activated=? LIMIT 1") or die(mysqli_error());
        $sql->bind_param("issi", $activated, $email, $hash, $not_activated);
        $result = $sql->execute();
        $sql->execute();
        header("location: message.php?msg=");
        exit();

//THE SAME ELSE STATEMENTS BELOW THIS, BUT THEY ARE NEVER REACHED
}

$username = $_POST['username'];
$password = $_POST['password'];
$email = $_POST['email'];
$gender = $_POST['gender'];
$profession = $_POST['profession'];
$ip = $_SERVER['REMOTE_ADDR'];
$password_hash = password_hash($password, PASSWORD_DEFAULT);
$hash = md5( rand(0, 1000) );
//HERE IS WHERE IT'S THE SAME

$stmt = $connection->prepare("INSERT INTO `users` (username, password, email, gender, profession, ip, hash) VALUES(?, ?, ?, ?, ?, ?, ?)");
$stmt ->bind_param("sssssss", $username, $password_hash, $email, $gender, $profession, $ip, $hash);
$result = $stmt->execute();
$stmt->execute(); //THIS EXECUTES FINE

if($result) {
    $successMessage = "Now check your inbox or junk folder for verification email.";
//BEGIN EMAIL CODE AFTER THIS. WORKS FINE.