SFTP - I can't say what's happening today, but 8 years ago this was the only channel available when I added an ACH payment system to B2B accounting system. 80 column text files SFTP'd overnight to the company's bank. I also had a couple of 200 page dead tree books on my desk describing the process & formats.
I joked that it was originally designed for delivery by telegraph. I'm still not convinced I was wrong.