We are using B2B 4.02 and TN 4.5. The B2B Server is setup in a Reverse Invoke configuration. But, now I realize that some of our customers want to FTP the documents. Has anyone solved this issue and guide me in how to route the documents FTPd to the Reverse Invoke Server (on a regular FTP port as I can’t setup a proxy port for FTP) to the internal server as the customers can’t directly access the Internal Server.
I appreciate any suggestions/comments.

Reverse Invoke only supports HTTP/HTTPS, not FTP, as you’ve figured out. I’m not aware of anyone who has made modified version to support FTP. A method that might work (I haven’t tried it) is to have the service on the FTP listener write the message back onto an HTTP port on the same Integration Server, where that HTTP listener is set up for reverse invoke. That way you wouldn’t need to figure out how to directly interact with the reverse invoke mechanism.

If it works, I’d love to hear about it.

Yes, that is exactly what I have impemented as a workaround. I have a custom service that listens on the FTP port and then simply resubmits the document on the proxy port. From there on, the document gets passed on to the Internal Server.