Verification of data submitted via API

When I manually upload a file, there is a “verify” data step. I can’t seem to figure out how to do that same step with an API. (Yes, I’m brand new at this).

What I want is to have the API reject all the input if there is an error (not happily munge only the parts it can). This feels like something basic and so easy it escapes me.

Thanks for not laughing too hard at my basic question. I swear I’ve been reading the documentation and have scanned the files here. My search foo is weak today, apparently.