And yet it is the only one you raised, and the only one I responded to in this thread. You are moving the goal posts. If these posts were legal briefs the judge would say you have waived the rest of your arguments and I would have won (Waiving arguments being the legal equivalent to moving goalposts).
But you seem to have interpreted the necessary condition that a work must be fixed in order to be eligible for copyright as "any fixed portion of a work is copyrightable." This is untrue both because being fixed is necessary but insufficient for copyright, and because tiny portions of a work aren't works in themselves. Also, I have not claimed that anything that might be called an API and is fixed is necessarily copyrightable. I only said what is definitely not copyrighted. So no goalposts have been moved, you just misunderstood the necessary condition and my point: Protocols (like algorithms), unlike code APIs (and programs), aren't fixed, and so cannot be copyrighted regardless of anything else that may or may not be. That some tiny portions of a protocol might be fixed does not change the status of the work.
> they are.
They most certainly are not. If you think REST protocols are like code APIs, you should be able to explain why algorithms are not copyrightable but programs are. The law already makes a distinction between those two, so you'll need to explain why that distinction does not apply for protocols vs. APIs.