curl --request POST \
  --url https://prod.featherhq.com/api/v1/email/drafts/{messageId}/approve \
  --header 'X-API-Key: <api-key>'

{
  "message": {
    "id": "<string>",
    "threadId": "<string>",
    "status": "<string>"
  },
  "sent": true,
  "providerMessageId": "<string>"
}