Constituents search POST needs a JSON body

For GiveCampus integrations and API.

For POST /api/v2/constituents/search, send a JSON object body, for example {"ids":["EXTERNAL_ID"]}, with Content-Type: application/json and the valid Bearer credential. The POST query reads filters from that body. Putting ids only in the query string with an empty body is not equivalent; this endpoint rejects a blank body. ids means the school's external identifier; gc_constituent_ids means GiveCampus person identifiers. Browser cookies are not needed for the bearer-authenticated endpoint. Successful submission is asynchronous: use the returned request ID to retrieve status and the eventual download URL. Keep credentials and cookies out of support examples.