Receipt
It remains to consider the Response from the server:
<Receipt version="1">
<ReceiptId> R20349143 </ReceiptId>
<Time> 123456789012345678 </Time>
<Transfer> . . . </Transfer>
<UserId> Erwin </UserId>
<Signature> Blob </Signature>
</Receipt>
The nature of any digital signature is not defined as yet...