My Mysqli code doesn't insert data in my database

Question

for some reason that i can't seem to find, i can't get my mysqli code to write in my database. The "echo $newUserResult." ".$fullName;" work fine. I am pretty new to coding and i have spent lot of time trying to troubleshoot this. I'm sorry for wasting your guys time but i just can't see why it doesn't work.

<-----     Data Base Connection     ----->

<?php

$serverName = "localhost";
$dbUsername = "root";
$dbPassword = "";
$dbName = "stw";

$conn = mysqli_connect($serverName, $dbUsername, $dbPassword, $dbName);

if (!$conn){
    die("Connection Failed: " . mysqli_connect_error());
}

<-----     My Code     ----->

<?php

if(isset($_POST["nameSubmit"])){

    session_start();
    $newUser = $_SESSION["newUser"];
    $firstName = $_POST["firstName"];
    $lastName = $_POST["lastName"];
    $fullName = $firstName." ".$lastName;
    $fullNameLength = strlen($fullName);

    require_once 'dbc-inc.php';
    require_once 'functions-inc.php';

    if(emptyNameInput($firstName, $lastName) !== false){
        header("location: ../profile.php?error=Emptynameinput");
        exit();
    }
    if(invalidNamelength($fullNameLength) !== false){
        header("location: ../profile.php?error=invalidnamelength");
        exit();
    }
    if(invalidName($firstName, $lastName) !== false){
        header("location: ../profile.php?error=invalidname");
        exit();
    }
    addName($conn, $newUser, $fullName);
}
else{
    header("location: ../profile.php");
}

<-----     addName Function     ----->

function addName($conn, $newUser, $fullName){

    $sql = "INSERT INTO users (unew, uname) VALUES (?, ?)";
    $stmt = mysqli_stmt_init($conn);

    if(!mysqli_stmt_prepare($stmt, $sql)){
        header("location: ../profile.php?error=namestmtfailed");
        exit();
    }

    $newUserResult = $newUser + 1;

    mysqli_stmt_bind_param($stmt, "is", $newUserResult, $fullName);
    mysqli_stmt_execute($stmt);
    echo $newUserResult." ".$fullName;
    exit();
}