curl --request PUT \
  --url https://app.lettr.com/api/templates/{slug} \
  --header 'Authorization: Bearer <token>' \
  --header 'Content-Type: application/json' \
  --data '
{
  "name": "Updated Welcome Email"
}
'

{
  "message": "Template updated successfully.",
  "data": {
    "id": 123,
    "name": "Updated Welcome Email",
    "slug": "welcome-email",
    "project_id": 5,
    "folder_id": 10,
    "active_version": 2,
    "merge_tags": [
      {
        "key": "NAME",
        "required": true
      }
    ],
    "created_at": "2026-01-15T10:00:00+00:00",
    "updated_at": "2026-01-28T14:30:00+00:00"
  }
}