Problem sending the form

Question

I have a problem making this short form website work he is sending the email on the console it gives that error:

line 2 code :

$("#submit_btn").click(function()...

follows my code: HTML:

<form id="form-elements" onSubmit="return false" class="form-inline text-center">
            <div class="row">
                <div class="col-md-12 center">
                    <div id="result"></div>
                </div>
            </div>

            <div class="form-group">
                  <input type="email" class="form-control email-input" placeholder="Digite seu e-mail" name="email"
                                       id="email" required>
                  <div id="gif" class="text-center" ></div>
            </div> 
            <button type="submit" class="btn btn-primary button-send" id="submit_btn">Quero anunciar meu serviço</button>
        </form>

JS:

//Contact Us
    $("#submit_btn").click(function() {
                //get input field values
                var user_email      = $('input[name=email]').val();

                //simple validation at client's end

                var post_data, output;
                var proceed = true;

                if(user_email==""){
                        proceed = false;
                }


                //everything looks good! proceed...
                if(proceed)
                {
                        //data to be sent to server
                        post_data = {'userEmail':user_email};

                        //Ajax post data to server
                        $("#gif").html('<img src="http://dev.cloudcell.co.uk/bin/loading.gif">');
                        $.post('contact.php', post_data, function(response){


                                //load json data from server and output message
                if(response.type == 'error')
                {
                    output = '<div class="alert-danger" style="padding:10px; margin-bottom:25px;">'+response.text+'</div>';
                }else{
                    output = '<div class="alert-success" style="padding:10px; margin-bottom:25px;">'+response.text+'</div>';

                    $("#gif").hide();
                    //reset values in all input fields
                    $('#form-elements input').val('');
                }

                $("#result").hide().html(output).slideDown();
                        }, 'json');

                }
        });

        //reset previously set border colors and hide all message on .keyup()
        $("#form-elements input, #form-elements").keyup(function() {
                $("#result").slideUp();
        });

PHP:

<?php
if($_POST)
{
    $to_Email       = "[email protected]"; //Replace with recipient email address
    $subject        = 'Contato - Página Konectah'; //Subject line for emails


    //check if its an ajax request, exit if not
    if(!isset($_SERVER['HTTP_X_REQUESTED_WITH']) AND strtolower($_SERVER['HTTP_X_REQUESTED_WITH']) != 'xmlhttprequest') {

        //exit script outputting json data
        $output = json_encode(
        array(
            'type'=>'error',
            'text' => 'Request must come from Ajax'
        ));

        die($output);
    }

    //check $_POST vars are set, exit if any missing
    if(!isset($_POST["userEmail"]))
    {
        $output = json_encode(array('type'=>'error', 'text' => 'Os campos de entrada estão vazios!  '));
        die($output);
    }

    //Sanitize input data using PHP filter_var().
    $user_Email       = filter_var($_POST["userEmail"], FILTER_SANITIZE_EMAIL);

    //additional php validation
    if(!filter_var($user_Email, FILTER_VALIDATE_EMAIL)) //email validation
    {
        $output = json_encode(array('type'=>'error', 'text' => 'Por favor ultilize um e-mail válido'));
        die($output);
    }

    $message_Body .= "<strong>Email: </strong>". $user_Email ."<br>";

    $headers = "From: " . strip_tags($user_Email) . "\r\n";
    $headers .= "Reply-To: ". strip_tags($user_Email) . "\r\n";
    $headers .= "MIME-Version: 1.0\r\n";
    $headers .= "Content-Type: text/html; charset=ISO-8859-1\r\n";



    //proceed with PHP email.
    $headers = 'From: '.$user_Email.'' . "\r\n" .
    'Reply-To: '.$user_Email.'' . "\r\n" .
    'X-Mailer: PHP/' . phpversion(). "\r\n" .
    'Content-type: text/html';



    $sentMail = @mail($to_Email, $subject, $message_Body, $headers);

    if(!$sentMail)
    {
        $output = json_encode(array('type'=>'error', 'text' => 'Ocorreu um erro tente novamente'));
        die($output);
    }else{
        $output = json_encode(array('type'=>'message', 'text' =>' Obrigado por sua inscrição retornaremos em breve'));
        die($output);
    }
}
?>