I am testing PayPal payments through Sandbox. So what do I do:

1. Make a payment from my Android device, using SDK AppID: "APP-80W284485P519543T".
2. Receive RESULT_OK in applicationResult and receive response on server side through IPN service.
3. Now I am taking all responce from IPN and send it to paypal verification sandbox server to verify payment. It cat return (VERIFIED or INVALID).

But the problem is that it is return INVALID. So whats can be the problem? What I am doing wrong? Thanks.

This is what I send to verify:

https://www.sandbox.paypal.com/cgi-bin/webscr?cmd=_notify-validate&payment_request_date=Mon+Mar+26+02%3A37%3A10+PDT+2012&fees_payer=EACHRECEIVER&transaction[0].is_primary_receiver=false&memo=Buy+1500+coins&transaction_type=Adaptive+Payment+PAY&verify_sign=AWimjEpfvS2eR6IgBwHtiwM0rMDUA.b2twU2ADjkAY-kg5szeluxcqKb&log_default_shipping_address_in_transaction=false&pay_key=AP-2YR77828AV574621G&transaction[0].amount=USD+1.99&reverse_all_parallel_payments_on_error=true&ipn_notification_url=http%3A%2F%2Fdev-vs.upiter.com%2Fvspayment%2Fproviders%2Fvs%2Ffb%2Fpaypalcallback&action_type=CREATE&notify_version=UNVERSIONED&transaction[0].status_for_sender_txn=Pending&test_ipn=1&cancel_url=https%3A%2F%2Fwww.paypal.com&transaction[0].pending_reason=UNILATERAL&status=COMPLETED&charset=windows-1252&transaction[0].paymentType=GOODS&request_body=&request_url=http%3A%2F%2Fdev-vs-mobile.stagika.com%2Fvspayment%2Fproviders%2Fvs%2Ffb%2Fpaypalcallback&return_url=https%3A%2F%2Fwww.paypal.com&transaction[0].receiver=a.merchant1.kv%40gmail.com&request_method=POST&transaction[0].id_for_sender_txn=0X355330VH030952T&sender.useCredentials=true