bootstrap formvalidation.io remote validator MySQL PHP

i'm having some issues getting a modal form validate a username from Mysql database using PHP.

here is my PHP script to validate the username, when i run it alone it works but when it will not get called from the remote validator.

PHP code :

checkUsername.php

            <?php

             $isAvailable = true;

             //get the username  and password
               $uname = trim($_POST['username']);
               $umail = trim($_POST['email']);

            //connect to database   
            require_once '/php-includes/dbconfig.inc.php';

                     $stmt = $DB_con->prepare("SELECT username, email FROM member WHERE username=:uname OR email=:umail");
                     $stmt->execute(array(':uname'=>$uname, ':umail'=>$umail));
                     $row=$stmt->fetch(PDO::FETCH_ASSOC);


                        if($row['username']==$uname) {
                            $isAvailable = false; 
                        }

                     // Finally, return a JSON
                echo json_encode(array('valid' => $isAvailable));
            ?>

and this is the formValidation.io script that i'm using from http://ift.tt/1OFKcKf

            $(document).ready(function() {
                $('#registerForm')
                    .formValidation({
                        framework: 'bootstrap',
                        icon: {
                            valid: 'glyphicon glyphicon-ok',
                            invalid: 'glyphicon glyphicon-remove',
                            validating: 'glyphicon glyphicon-refresh'
                        },
                        fields: {
                            userName: {
                                validators: {
                                    notEmpty: {
                                        message: 'The user name is required'
                                    },
                                    remote: {
                                        url: 'checkUsername.php'
                                    }
                                }
                            }
                        }
                    })
                    // This event will be triggered when the field passes given validator
                    .on('success.validator.fv', function(e, data) {
                        // data.field     --> The field name
                        // data.element   --> The field element
                        // data.result    --> The result returned by the validator
                        // data.validator --> The validator name

                        if (data.field === 'userName'
                            && data.validator === 'remote'
                            && (data.result.available === false || data.result.available === 'false'))
                        {
                            // The userName field passes the remote validator
                            data.element                    // Get the field element
                                .closest('.form-group')     // Get the field parent

                                // Add has-warning class
                                .removeClass('has-success')
                                .addClass('has-warning')

                                // Show message
                                .find('small[data-fv-validator="remote"][data-fv-for="userName"]')
                                    .show();
                        }
                    })
                    // This event will be triggered when the field doesn't pass given validator
                    .on('err.validator.fv', function(e, data) {
                        // We need to remove has-warning class
                        // when the field doesn't pass any validator
                        if (data.field === 'userName') {
                            data.element
                                .closest('.form-group')
                                .removeClass('has-warning');
                        }
                    });
            });
            </script>