curl -X POST https://api.v2.dealmachine.com/v1/mail/campaigns/a1b2c3d4/send \
  -H "Authorization: Bearer dm_sk_live_xxx"

{
  "data": {
    "id": "a1b2c3d4-e5f6-7890-abcd-ef1234567890",
    "status": "active",
    "total_recipients": 150,
    "launched_at": "2026-03-11T14:23:45Z"
  }
}

{
  "error": {
    "code": "insufficient_credits",
    "message": "Insufficient wallet credits to launch this campaign",
    "request_id": "req_abc123",
    "details": {
      "required_cents": 10800,
      "available_cents": 5000,
      "shortfall_cents": 5800
    }
  }
}