Blockchain.info - How to reply to a sender in a callback? I just started using the Blockchain.info API, I've set it up to notify me when a payment is made, however all addresses in the callback are the destination address. Shouldn't I have the senders address as well?

Is there any way of getting the senders address, otherwise how am I supposed to reply?

I know transaction has the address, do I just pull the first address from inputs of the transaction?
You would need to fetch the transaction using the /rawtx call and use one of those inputs.

However you should not send a refund back to the the sending address unless the user has specifically told this is what will happen as shared wallets cannot receive coins back to the sending address.