Required inputs for a schema

Returns the input keys this schema declares: those required to submit a request against it, and those it accepts but does not require. Field names are returned verbatim. Use them as the keys of the inputs object on POST /v1/requests. Lists are sorted. Neither list constrains inputs: additional keys outside both are accepted and passed to the call as context. This is the baseline: if your account is enabled for per-payer required inputs, some payers require additional fields not listed here, reported as INVALID_INPUTS on POST /v1/requests.