Sandbox subject conflict

{
  "type": "https://docs.get-exo.com/errors/sandbox_subject_conflict",
  "title": "Sandbox subject conflict",
  "status": 409,
  "detail": "The reserved sandbox subject id is taken by a regular subject.",
  "code": "sandbox_subject_conflict",
  "requestId": "req_9f2c41ab7d0e5c18"
}