Am trying to get json data success response but i got error

please help me I am a junior my code is not good I need to get a JSON response for each successfully sent message. I can send the SMS successfully but I can’t get a success message from send_sms.php

<!-- index.php --->
<div id="responce"></div> <!-- respond sms sending -->
<form method="POST" onclick="return false">
<div class="form-group">
    <label>Your Message</label>
<textarea class="form-control" rows="4" cols="100" id="message"
name="message" maxlength="70" required></textarea>
</div>
<button class="btn btn-primary" type="submit" name="submit"
onmousedown="start_sendig();" class="btn">Send</button>
</form>

enter image description here

//sendsms_button.js

function start_sendig() {
  $("#responce").html("Please wait sending on process");
  var message = $("#message").val();
  var path_uri = "sms/send_sms.php";

  $.ajax({
    type: "POST",
    url: path_uri,
    data: {
      message: message,
    },
    success: function (data) {
      var json = $.parseJSON(data);

      if (json.response == "success") {
        $("#responce").html(
          "Message Sent Successfully to " + json.current + " !!"
        );
      } else {
        $("#responce").html("Error to Sent " + json.current + " !!");
      }
    },
  });
}

Ajax shows this error

 caught SyntaxError: Unexpected end of JSON input
    at Function.parse [as parseJSON] (<anonymous>)
    at Object.success (sendsms_button.js:13:20)
    at i (jquery-3.2.1.min.js:2:28017)
    at Object.fireWith [as resolveWith] (jquery-3.2.1.min.js:2:28783)
    at A (jquery-3.2.1.min.js:4:14035)
    at XMLHttpRequest.<anonymous> (jquery-3.2.1.min.js:4:16323)

<?php
//send_sms.php
   
include ("vendor/autoload.php");
include ("../config.php");


//insert record
$msg_sms = $_POST['message'];
mysqli_query ($con, "insert into sent_sms (message) values ('$msg_sms')");
if (isset($_POST['submit'])){
//select numbers
$result = mysqli_query($con, "SELECT mphone FROM members");
while ($row = mysqli_fetch_array($result)){
$numbers = $row['mphone'];

    foreach (explode("+", $numbers) as $phone) {
    $basic  = new VonageClientCredentialsBasic("fxxxxx", "xxxxxxxxxxxxx");
    $client = new VonageClient($basic);

    $response = $client->sms()->send(
    new VonageSMSMessageSMS($phone, 'Hotel', $msg_sms)
    );

    $message = $response->current();

        if ($message->getStatus() == 0) {
            $data = array(
                    "response" => "success",
                    "current" => '+' . $phone
                );

                echo json_encode($data);
        } else {
        echo "<script>alert('The message failed with status: " . $message->getStatus() . "');</script>";
        }
    }
}

}
   
 
?>

my goal is to show each success message like Sending to +125332626 success