RD Web Access Help. Remoteapp setup is apparently incomplete on Server 2012

Kind of support: Software
Description of support work: I have set up Server 2012 and have remoteapp stuff running fine within the LAN. I can connect remotely, Sign in and select an app. The connectoid is downloaded and, on opening it, I am again invited to log in, at which point the dialogue box indicates it's connecting to the server to start the app. However, no further progress is made and, after perhaps five seconds, the dialogue box disappears and no application window appears.
Extra notes: I thought this might be because I couldn't connect on ports other than 443 so I set up the RD gateway on the server but it made no difference. I think I just need someone who's a bit more familiar than I with setting up this functionality. Someone who can with some justification call themselves expert, perhaps. If that's you, I think the job will be very quick and easy. I would expect it to take well under an hour, unless I've got completely the wrong end of the stick about what's going on.

I can give you TeamViewer access to the server and credentials to log in via the Web -- and anything else you need. Budget could be slightly negotiable but I think you can probably get the job done in half an hour, if you're the one I'm looking for.