Signup success but not submitting user input to database - PHP

Question

I want to submit data using this simple form using php and html. My database table is called users with the following attributes:

usersId 
usersName,
usersEmail,
usersUid,
usersPwd

After filing the form , it seems to not have any error but it does not send the data to the database.

functions.inc.php

<?php

function emptyInputSignup($name,$email,$username,$pwd,$pwdRepeat) {
    $result;
    if (empty($name) || empty($email) || empty($username) || empty($pwd) || empty($pwdRepeat)) {
        $result = true;
    } else {
        $result = false;
    }
    return $result;
}

function invalidUid($username) {
    $result;
    if (preg_match('/^[a-z]((?!__)[a-z\d_])+[a-z\d]$/i', $username)) {
        $result = true;
    } else {
        $result = false;
    }
    return $result;
}

function invalidEmail($email) {
    $result;
    if (!filter_var($email, FILTER_VALIDATE_EMAIL)) {
        $result = true;
    } else {
        $result = false;
    }
    return $result;
}

function pwdMatch($pwd, $pwdRepeat) {
    $result;
    if ($pwd !== $pwdRepeat) {
        $result = true;
    } else {
        $result = false;
    }
    return $result;
}

function uidExists($conn, $username, $email) {
    $sql = "SELECT * FROM users WHERE usersUid = ? OR usersEmail = ?;";
    $stmt = mysqli_stmt_init($conn);
    if (!mysqli_stmt_prepare($stmt, $sql)) {
        header("location: ../signup.php?error=stmtfailed");
        exit();
    }

    mysqli_stmt_bind_param($stmt, "ss", $username, $email);
    mysqli_stmt_execute($stmt);

    $resultData = mysqli_stmt_get_result($stmt);

    if ($row = mysqli_fetch_assoc($resultData)) {
        return $row;
    } else {
        $result = false;
        return $result;
    }
    mysqli_stmt_close($stmt);
}

function createUser($conn, $name, $email, $username, $pwd) {
    $sql = "INSERT INTO users (usersName, usersEmail, usersUid, usersPwd) VALUES (?, ?, ?, ?);";
    $stmt = mysqli_stmt_init($conn);
    if (!mysqli_stmt_prepare($stmt, $sql)) {
        header("location: ../signup.php?error=stmtfailed");
        exit();
    }

    $hashedpwd = password_hash($pwd, PASSWORD_DEFAULT);

    mysqli_stmt_bind_param($stmt, "ssss", $name, $email, $username, $hashedpwd);
    mysqli_stmt_execute($stmt);
    mysqli_stmt_close($stmt);
    header("location: ../signup.php?error=none");
    exit();
}

signup.inc.php

<?php

if (isset($_POST["submit"])){
    
    $name = $_POST["name"];
    $email = $_POST["email"];
    $username = $_POST["uid"];
    $pwd = $_POST["pwd"];
    $pwdRepeat = $_POST["pwdrepeat"];

    require_once 'dbh.inc.php';
    require_once 'functions.inc.php';

    if(emptyInputSignup($name,$email,$username,$pwd,$pwdRepeat) !== false){
        header("location: ../signup.php?error=emptyinput");
        exit();
    }

    if(invalidUid($username) !== false){
        header("location: ../signup.php?error=invaliduid");
        exit();
    }

    if(invalidEmail($email) !== false){
        header("location: ../signup.php?error=invalidemail");
        exit();
    }

    if(pwdMatch($pwd, $pwdRepeat) !== false){
        header("location: ../signup.php?error=pwddontmatch");
        exit();
    }

    if(uidExists($conn, $username, $email) !== false){
        header("location: ../signup.php?error=usernametaken");
        exit();
    }

    createUser($conn, $name, $email, $username, $pwd);

}
else {
    header("location:../signup.php?error=none");
    exit();
}