Registrierung

// Check input errors before inserting in database
    if(empty($username_err) && empty($nname_err) && empty($vname_err) && empty($password_err) && empty($confirm_password_err)){

        // Prepare an insert statement
        $sql = "INSERT INTO users (username, vname, nname, password) VALUES (?, ?, ?, ?)";

        if($stmt = mysqli_prepare($link, $sql)){
            // Bind variables to the prepared statement as parameters
            mysqli_stmt_bind_param($stmt, "ssss", $param_username, $param_vname, $param_nname, $param_password);

            // Set parameters
            $param_username = $username;
            $param_vname = $vname;
            $param_nname = $nname;
            $param_password = password_hash($password, PASSWORD_DEFAULT); // Creates a password hash

            // Attempt to execute the prepared statement
            if(mysqli_stmt_execute($stmt)){
                // Redirect to login page
                header("location: bla.php");
            } else{
                echo "Something went wrong. Please try again later.";
            }
        }

        // Close statement
        mysqli_stmt_close($stmt);     <--- Das ist die Betroffene Zeile 165 die den Fehler verursacht!
    }

    // Close connection
    mysqli_close($link);
}
?>