RESTful API guidelines historically have encouraged snake case. camel case has started to be more prolific so it's an equally good option but I've been on a support call at least twice where someone had improper case for a JSON field and it led to debugging an issue that would not have been an issue with snake case.
I should also mention that snake case has been the case type for many ruby, perl and python based RESTful APIs and the things you've listed are JS based and tools.
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