I recall in about 2009 working on a project where the clients inventory system ran on an AS/400 and I knew literally nothing about IBM mainframes at the time. All we wanted was them to publish a simple JSON API we could poll hourly to update the front end we were building. In a conference call with umpteen of their engineers, they basically told us that was impossible. I thought this was ridiculous, but they were insistent.
Their counter proposal was that they would automate emailing us updates and we could parse and process those. I still have no clue how that could be easier for them but it sure would have been more work and infrastructure for us!
Eventually after literally weeks of back and forth they finalized landed on letting us use FTP to read hundreds of XML files they would generate nightly. They were often mildly malformed/improperly encoded. It was simpler to deal with that than ask them to fix it. It was not a very fun project, but a major learning experience looking back.
I was a young hotshot who had only recently been promoted to lead developer, and having to interact with these people who clearly thought I was dumb for not knowing anything about IBM mainframes certainly knocked me down a peg. Kind of humbling to see you don't know what you don't know once in a while.