Queues the campaign for processing and returns immediately — the campaign is not yet running when the 202 is returned. Poll GET /campaign/{id} and watch for status: "running".

This endpoint also acts as a resume endpoint: if the campaign is currently paused, calling this endpoint resumes it (status transitions from paused → running).

{
  "status": true,
  "data": {
    "message": "Campaign is being processed"
  }
}