I need to click on the button to send some data to the php file and update the user's balance in the database.

quotes.js Part of the code:

var data = {
    sell: sell_current_quote,
    buy: bue_current_quote
};
$.ajax({
    type: 'POST',
    url: '/wp-content/themes/NAME/page-trading.php',
    dataType: 'json',
    data: data,
    success: function(my_data) {
        alert('Ok');
    }
});

page-trading.php Part of the code:

if( isset($_POST['sell']) && isset($_POST['buy']) ) {

$sell = json_decode($_POST['sell']);
$buy = json_decode($_POST['buy']);

global $wpdb, $userdata;

$wpdb->update( PREF .'users_balance', 
    array(
        'user_balance_2' => 100
    ), 
    array(
        'user_id'      => $userdata->id,
        'user_schet_2' => 00000001,
    ), 
    array("%d","%d")
);

die();
}

As a result, the database is not updated. in the console, in data headers come about sell: 0.99788 buy: 0

Tell me, please, how to do it right?