googleScript.js

var sheetName = 'leads1'
var scriptProp = PropertiesService.getScriptProperties()

function initialSetup(){
    var activeSpreadsheet = SpreadsheetApp.getActiveSpreadsheet()
    scriptProp.setProperty('key', activeSpreadsheet.getId())
}

function doPost(e){
    var lock = LockService.getScriptLock()
    lock.tryLock(10000)

    try{
        var doc = SpreadsheetApp.openById(scriptProp.getProperty('key'))
        var sheet = doc.getSheetByName(sheetName)

        var headers = sheet.getRange(1, 1, 1, sheet.getLastColumn()).getValues()[0]
        var nextRow = sheet.getLastRow() + 1

        var newRow = headers.map(function(header){
            return header === 'timestamp' ? new Date() : e.parameter[header]
        })

        sheet.getRange(nextRow, 1, 1, newRow.length).setValues([newRow])

        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()
    }
}