Xcart and payment gateway advice

We are implementing a payment gateway (Raven/Pacnet) into Xcart which involves posting the data to an offsite gateway. We have the files that talk to Raven which need to be called using an ajax post call, evaluate the result from raven and then take you to the xcart callback url to process the payment and put xcart in the right state. We now need to know what the callback URL is for [login to view URL] are happy to pay someone for this knowledge and some support like answering a few questions. If you have general experience using software other than Xcart DO NOT REPLY, these are not skills that can be generalised from other cart software. To prove that you have read this specification properly, respond with the title 'blue M&Ms' or mention that phrase in your response. Do not send me endless copied and pasted lists of work you allege you have done, this is spam and I will report you.