For Creating auto number on spreadsheet.

create-autonumber-on-spreadsheet.ts

function onFormSubmit(e) {
  var sheet = SpreadsheetApp.getActiveSpreadsheet().getActiveSheet();
  var lastRow = sheet.getLastRow();

  
  var serial = lastRow - 1; 
  var serialNumber = ('000' + serial).slice(-3);

 
  var today = new Date();
  var month = ('0' + (today.getMonth() + 1)).slice(-2); 
  var year = today.getFullYear();

 
  var numberFormat = `${serialNumber}/QA/RPAY/${month}/${year}`;

  sheet.getRange(lastRow, 1).setValue(numberFormat);
}