HTTP/JSON API works too, but you can assume it's what they mean by REST.
It makes me wish we stuck with XML based stuff, it had proper standards, strictly enforced by libraries that get confused by things not following the standards. HTTP/JSON APIs are often hand-made and hand-read, NIH syndrone running rampant because it's perceived to be so simple and straightforward. To the point of "we don't need a spec, you can just see the response yourself, right?". At least that was the state ~2012, nowadays they use an OpenAPI spec but it's often incomplete, regardless of whether it's handmade (in which case people don't know everything they have to fill in) or generated (in which case the generators will often have limitations and MAYBE support for some custom comments that can fill in the gaps).
It makes me wish we stuck with XML based stuff, it had proper standards, strictly enforced by libraries that get confused by things not following the standards. HTTP/JSON APIs are often hand-made and hand-read, NIH syndrone running rampant because it's perceived to be so simple and straightforward. To the point of "we don't need a spec, you can just see the response yourself, right?". At least that was the state ~2012, nowadays they use an OpenAPI spec but it's often incomplete, regardless of whether it's handmade (in which case people don't know everything they have to fill in) or generated (in which case the generators will often have limitations and MAYBE support for some custom comments that can fill in the gaps).