CreateAccount.php

<?php
require_once("ITConnection.php");

$username = $_GET["username"];
$NFCUID = $_GET["NFCUID"];

$username = filter_var($username, FILTER_SANITIZE_STRING);
$NFCUID = filter_var($NFCUID, FILTER_SANITIZE_STRING);
$lapCount = 0;

$sql = "INSERT INTO Users(Username, NFCUID) VALUES ('$username', '$NFCUID') ON DUPLICATE KEY UPDATE LapCount='$lapCount', NFCUID='$NFCUID';";

if ($conn->query($sql) === FALSE) {
    echo("Db write failed.");
} else{
    echo("Added entry");
}

$conn->close();
?>