Google Script Error on Post

Question

I am posting data to google sheets using php, everytime I post the data it get added on the sheet correctly, but i get the error message as

We8d#39;re sorry, a server error occurred. Please wait a bit and try again.

My php curl post code is:

 $ch = curl_init();
 curl_setopt($ch, CURLOPT_URL, $gsurl);
 curl_setopt($ch, CURLOPT_POST, true);
 curl_setopt($ch, CURLOPT_POSTFIELDS, $data);
 $output = curl_exec($ch);
 $info = curl_getinfo($ch);
 curl_close($ch);

$res = json_decode($output, 1);

My GS App Script is :

var SCRIPT_PROP = PropertiesService.getScriptProperties(); // new property service


function doGet(e){
  return handleResponse(e);
}

function doPost(e){
  return handleResponse(e);
}

function handleResponse(e) {
  var lock = LockService.getPublicLock();
  lock.waitLock(30000); 

  try {

    var doc = SpreadsheetApp.openById(SCRIPT_PROP.getProperty("key"));
    var sheet = doc.getSheetByName(SHEET_NAME);


    var headRow = e.parameter.header_row || 1;
    var headers = sheet.getRange(1, 1, 1, sheet.getLastColumn()).getValues()[0];
    var nextRow = sheet.getLastRow()+1; 
    var row = []; 

    for (i in headers){
      if (headers[i] == "Timestamp"){ 
        row.push(new Date());
      } else { 
        row.push(e.parameter[headers[i]]);
      }
    }

    sheet.getRange(nextRow, 1, 1, row.length).setValues([row]);
    // return json success results
    return ContentService
          .createTextOutput(JSON.stringify({"result":"success", "row": nextRow}))
          .setMimeType(ContentService.MimeType.JSON);
  } catch(e){

    return ContentService
          .createTextOutput(JSON.stringify({"result":"error", "error": e}))
          .setMimeType(ContentService.MimeType.JSON);
  } finally { 
    lock.releaseLock();
  }
}

function setup() {
    var doc = SpreadsheetApp.getActiveSpreadsheet();
    SCRIPT_PROP.setProperty("key", doc.getId());
}

Please help me.