How to retain users when payment is *not* the last part of the process?

I'm working on a project in government that requires users to fill in an online form and make payment for the service online, but that's not the end — users then have to do some stuff in the real world, including downloading and printing some now-finalised documents, and taking them to the appointment they've booked as part of the online application process.

The problem: in online transactions (most typically shopping), payment is almost always the last thing you do, to the point where the research participants we've tested with tend to switch off when they see that their (pretend) payment has been successful. It's vital that we retain users: while they might think the 'conversation' is over after payment, we know it isn't, and there's some important information after payment that we don't want them to miss.

(NB: it would be inappropriate to put the information before payment, because (a) it's not relevant yet, being about what they need to do next, and (b) users can change their form details at anytime up to making payment successfully, so we don't want them to download any documents until the details they've given can no longer be changed)

Are there any examples out there (ideally good ones, but I'll take what I can get) of online processes where payment is not the last thing? Or any tricks to stop people from dropping out? This isn't e-commerce in its usual sense; the experience will be worse for everyone (customers and government) if customers pay but don't see the information after that about what they need to do next.

Thanks in advance :)