edit

<?php
include 'dbconnect.php';
$user = '';
if(isset($_POST['userId']) && !empty($_POST['userId']))
{
    $user = $_POST['userId'];
}

$sql = "SELECT * FROM users WHERE userId = '$user' ";
$query = mysqli_query($conn, $sql);

if($query)
{
    $data = mysqli_fetch_assoc($query);
    echo json_encode($data);
}

?>