我已经创建了一个客户端地址簿，但是似乎不能添加新的客户端

我已经为我的客户端应用程序创建了一个地址簿。我可以登录和退出。当我点击刷新，重定向重新登录时，浏览器不会记住数据，所有这些都很好，但是添加下面的文件后要添加新的客户端。我不能这样做。有人可以帮助我确定为什么我不能成功添加新客户吗?

<?php
session_start();
// if user is not logged in
if(!$_SESSION['loggedInUser']) {
    // send them to the login page
    header("Location: index.php");
}
// connect to the database
include('includes/connection.php');
// include functions file
include('includes/functions.php');
// if add button was submitted
if(isset($_POST['add'])) {
    // set all variables to empty by default
    $clientName = $clientEmail = $clientPhone = $clientAddress =$clientCompany = $clientNotes = "";
    // check to see if inputs are empty
    // create variables with form data
    // wrap the data with our function
    if($_POST["clientName"]) {
        $nameError = "Please enter a name <br>";
    } else {
        $clientName = validateFormData($_POST["clientName"]);
    }
    if($_POST["clientEmail"]) {
        $emailError = "Please enter a email <br>";
    } else {
        $clientEmail = validateFormData($_POST["clientEmail"]);
    }
    // these inputs are not required
    // so we'll just store whatever has been entered
    $clientPhone    = validateFormData($_POST["clientPhone"]);
    $clientAddress    = validateFormData($_POST["clientAddress"]);
    $clientCompany    = validateFormData($_POST["clientCompany"]);
    $clientNotes    = validateFormData($_POST["clientNotes"]);
    // if required fields have data
    if($clientName && $clientEmail) {
        // create query
        $query = "INSERT INTO client(id, name, email, phone, address, company, notes, date_added) VALUES(NULL, '$clientName', '$clientEmail', '$clientPhone', '$clientAddress', 'clientCompany', 'clientNotes', CURRENT_TIMESTAMP)";
        $result = mysqli_query($conn, $query);
        // if query was successful
        if($result) {
            // refresh page with query string
            header("Location: clients.php?alert=success");
        } else {
            // something went wrong
            echo "Error: ".$query."<br>".mysqli_error($conn);
        }
    }
}
// close the mysql connection
mysqli_close($conn);

include('includes/header.php');
?>
<h1>Add Client</h1>
<form action="<?php echo htmlspecialchars($_SERVER['PHP_SELF']); ?>" method="post" class="row">
    <div class="form-group col-sm-6">
        <label for="client-name">Name *</label>
        <input type="text" class="form-control input-lg" id="client-name" name="clientName" value="">
    </div>
    <div class="form-group col-sm-6">
        <label for="client-name">Email *</label>
        <input type="text" class="form-control input-lg" id="client-email" name="clientEmail" value="">
    </div>
    <div class="form-group col-sm-6">
        <label for="client-phone">Phone</label>
        <input type="text"
 class="form-control input-lg" id="client-phone" name="clientPhone" value="">
    </div>
    <div class="form-group col-sm-6">
        <label for="client-address">Address</label>
        <input type="text" class="form-control input-lg" id="client-address" name="clientAddress" value="">
    </div>
    <div class="form-group col-sm-6">
        <label for="client-company">Company</label>
        <input type="text" class="form-control input-lg" id="client-company" name="clientCompany" value="">
    </div>
    <div class="form-group col-sm-6">
        <label for="client-notes">Notes</label>
        <textarea type="text" class="form-control input-lg" id="client-notes" name="clientNotes"></textarea>
    </div>
    <div class="col-sm-12">
        <a href="clients.php" type="button" class="btn btn-lg btn-default">Cancel</a>
        <button type="submit" class="btn btn-lg btn-success pull-right" name="add">Add Client</button>
    </div>
</form>
<?php
include('includes/footer.php');
?>