curl --request POST \
  --url https://api.railmail.app/api/v1/campaigns/{campaignKey}/send \
  --header 'X-API-Key: <api-key>'

{
  "id": "3c90c3cc-0d44-4b50-8888-8dd25736052a",
  "campaignKey": "<string>",
  "name": "<string>",
  "subject": "<string>",
  "previewText": "<string>",
  "contentJson": "<string>",
  "contentText": "<string>",
  "status": "<string>",
  "sendStrategy": "<string>",
  "topicIds": [
    "3c90c3cc-0d44-4b50-8888-8dd25736052a"
  ],
  "segmentIds": [
    "3c90c3cc-0d44-4b50-8888-8dd25736052a"
  ],
  "estimatedRecipientCount": 123,
  "scheduledAt": "2023-11-07T05:31:56Z",
  "completedAt": "2023-11-07T05:31:56Z",
  "fromEmail": "<string>",
  "fromName": "<string>",
  "preSendScore": 123,
  "preSendStatus": "<string>",
  "createdAt": "2023-11-07T05:31:56Z",
  "updatedAt": "2023-11-07T05:31:56Z"
}