curl --request POST \
  --url https://app.lettr.com/api/templates \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "name": "Welcome Email",
  "json": "{\"tagName\":\"mj-container\",\"children\":[{\"tagName\":\"mj-text\",\"content\":\"Hello {{FIRST_NAME}}!\"}]}"
}
'

{
  "message": "Template created successfully.",
  "data": {
    "id": 123,
    "name": "Welcome Email",
    "slug": "welcome-email",
    "project_id": 5,
    "folder_id": 10,
    "active_version": 1,
    "merge_tags": [
      {
        "key": "FIRST_NAME",
        "required": true
      }
    ],
    "created_at": "2026-01-28T12:00:00+00:00"
  }
}