Answer
For a straightforward JSON payload, putting a validated JSON structure directly in the event action's Body tab — using the standard &FIELD_NAME (or &NEW:FIELD_NAME) substitution syntax for the values you need to send — is generally sufficient on its own, without necessarily needing anything set in Additional Headers or Query Parameters unless the target endpoint specifically requires them (like an auth header or a query-string parameter); start with a validated Body payload first before assuming headers or query parameters are required.