AJAX将数据发送到PHP文件，但PHP无法从$ _POST获取数据

I am making a page on a website in PHP where a user fills out 3 fields and hits submit. The submit button should call my AJAX function to send the data to a database connection PHP file. I can confirm the data is sent from AJAX (via an alert) and the function returns a Success. This must mean my database query file is not interpreting the data correctly. Please help me understand where I went wrong.

Code from php page where the form is:

<script type="text/javascript">
function storeInvoice() {
    //var c_name = document.getElementById('c_name');
    //var c_license = document.getElementById('c_license');                         
    //var c_licenseemail = document.getElementById('c_licenseemail');
    var data=$('#myForm').serialize();
        $.ajax({
        url: "/paydb.php",
        type: "POST",
        data: data,
        async:false,
        dataType:'html',
        success: function (value) {
            alert("Sent: "+data);
        }
    });
}
</script>

Relevant Code from Database php file:

mysqli_select_db($conn, "main_db" );

$c_license = $_POST['c_license'];
$c_name = $_POST['c_name'];
$c_licenseemail = $_POST['c_licenseemail'];

//Another method was attempted below.
//$data=$_POST['serialize'];
//$c_licenseemail = $data['c_licenseemail'];
//$c_license = $data['c_license'];
//$c_name = $data['c_name'];

$query = "INSERT INTO `invoices`(`company`, `licensenum`, `licenseemail`) VALUES ('$c_name','$c_license','$c_licenseemail');";
mysqli_query($conn, $query);

The data is sent as:

c_name=testname&c_license=3&c_licenseemail=testemail%40email.com

Any help is much appreciated!

Please use the

mysqli_query($conn, $query) or die(mysqli_error($conn));

For duplicate key, you need to make the primary key to auto increment in your database.

In your success callback function replace alert(data) with alert(value) and in your database.php file echo any of the post variables to just check whether the values are correctly sent to database.php via ajax post.