Thanks for flagging this, this value genuinely isn’t retrievable from A004.
The eRSReviewReason-1 code system used here is a static, fixed set of codes rather than dynamic reference data. A004 only serves dynamic codeSystemType values such as SPECIALTY, CLINIC-TYPE, APPOINTMENT-CANCELLATION-REASON etc.
Instead, the full set of possible codes for eRS-ReviewReason-1 is documented directly in the OAS Specification itself, whenever a “reason” field can appear. The complete fixed list isshown in the “code: enum” section below:
We’d recommend hard coding these four values on your side rather than trying to resolve them via A004, the spec’s enum definition for this field is the source of truth and wont need a reference data lookup.