PayPal - Adaptive Payment: how do I know PaymentId on Success page?

Question

I use PayPal Adaptive Payments SDK for .NET and I try to implement simple payment. There is the following flow:

• Create simple payment (PayRequest) and get payment KEY (here I specify returnUrl as http://bla-bla-bla.com?invoiceId=567)
• Redirect user to PayPal with url
  https://www.sandbox.paypal.com/webscr?cmd=_ap-payment&paykey=[KEY]
• after user logged in to PayPal and confirm payment - PayPal redirects me to success page http://bla-bla-bla.com?invoiceId=567

The problem is there is no way to add some customer data to PayRequest object. And I do not know how to get transactionId on success page, because we initialize PayRequest.ReturnUrl before transaction created.
How can I get transactionId on success page? Thank you.

Answer 1

in your return url you can add your query string data as transactionId, then paypal will return to this url, so you can easily grab your transactionId