Why Google App Script Executing Multiple Time?

I created below code for capturing some data from webhooks and recording into google sheet + sending emails. Everything working fine. But code is executing multiple time. And executing after a random interval of time again and again.

Help me to solve the issue. Why its executing again and again.

All Required details are as below:

Click here to see Execution Screenshot.

Click here to see Screenshot from Google Sheet.

My Code is Below:

 //this is a function that fires when the webapp receives a GET request
    function doGet(e) {
      return HtmlService.createHtmlOutput("request received");
    }
    
    function doPost(e) {
      var jsonString = e.postData.getDataAsString();
      var myData = JSON.parse(jsonString);
      var email = myData.payload.payment.entity.email;
      var contact = myData.payload.payment.entity.contact;
      var amount = myData.payload.payment.entity.amount;
      var paymentid = myData.payload.payment.entity.id;
      var orderid = myData.payload.payment.entity.order_id;
      var sheet = SpreadsheetApp.getActiveSheet();
      var lastRow = Math.max(sheet.getLastRow(),1);
      sheet.insertRowAfter(lastRow);
      var currentTime = new Date();
      var trimname = email.substring(0, 5);
      var subject = "Download Starter E-Book";
      var description = "Please find attachment of Book and Invoice"; 
      var docFile = DriveApp.getFileById("1PD628HNgP4XO1Cy37DEGWi50OPK0iwq_K-HzlLfPhc0");
      var docpdfFile = DriveApp.getFileById("1vPhguJJfaXflxKVzwuUzZsNk3ZC9fBqV");
      var tempFolder = DriveApp.getFolderById("1UmqqjC35t0Zxu4ULcoDelsoZBW-NpHtM");
      var pdfFolder = DriveApp.getFolderById("1Mvwx54H3lccPDLDxSpYZ5ir83Ylq3gUK");
      var tempFile = docFile.makeCopy(tempFolder);
      var tempDocFile = DocumentApp.openById(tempFile.getId());
      var body = tempDocFile.getBody();
      body.replaceText("{name}", trimname);
      body.replaceText("{time}", currentTime);
      body.replaceText("{email}", email);
      body.replaceText("{contact}", contact);
      body.replaceText("{orderid}", orderid);
      body.replaceText("{payid}", paymentid);
      body.replaceText("{invoice}", paymentid);
      tempDocFile.saveAndClose();
      var pdfContentBlob = tempFile.getAs(MimeType.PDF);
      var finalpdfFile = pdfFolder.createFile(pdfContentBlob).setName(paymentid);
    GmailApp.sendEmail(email, subject, description, { attachments: [finalpdfFile, docpdfFile], name: 'Book Centre'});
        
      sheet.getRange(lastRow + 1, 1).setValue(currentTime);
      sheet.getRange(lastRow + 1, 2).setValue(email);  
      sheet.getRange(lastRow + 1, 3).setValue(contact);  
      sheet.getRange(lastRow + 1, 4).setValue(amount/100); 
      sheet.getRange(lastRow + 1, 5).setValue(paymentid); 
      sheet.getRange(lastRow + 1, 6).setValue(orderid); 
      
      SpreadsheetApp.flush();
      return HtmlService.createHtmlOutput("post request received");
    }

//--------------// Updates...

I have verified that webhook triggering once. I parallelly connected the webhook validator and found my Razorpay account is triggering once time.

I trigger 5 times from Razorpay. Webhook Validator capture it 5 times. but Google AppScript captures it multiple times.

One more thing I observed is that Every time Google Script is capturing different data but validator is capturing the same data in a good way. All reference screenshot is attached below.

Razorpay Webhook Configuration: Screenshot

Webhook Validator: Screenshot

Google App Script Execution: Screenshot