title: Checking the txn_id for preventing frauds
body: <p>If the payment status in "VERIFIED" then I'll just check if the txn_id exists(using sql) if it doesn't exist then I will continue checking the payment BUT if the txn_id exists it won't continue.</p>
  
  <p>Is this checking method correct for the txn_id in order of preventing a fraud?</p>
  
  <p>Thanks in advance,</p>