curl --request POST \
  --url https://api.railmail.app/api/v1/topics \
  --header 'Content-Type: application/json' \
  --header 'X-API-Key: <api-key>' \
  --data '
{
  "name": "<string>",
  "description": "<string>",
  "doubleOptInEnabled": true,
  "icon": "<string>"
}
'

{
  "topicKey": "<string>",
  "name": "<string>",
  "description": "<string>",
  "status": "<string>",
  "doubleOptInEnabled": true,
  "subscriberCount": 123,
  "activeSubscriberCount": 123,
  "createdAt": "2023-11-07T05:31:56Z"
}