curl --request GET \
  --url https://api.ngrok.com/backends/tunnel_group \
  --header 'Authorization: Bearer <token>' \
  --header 'ngrok-version: <ngrok-version>'

{
  "backends": [
    {
      "id": "<string>",
      "uri": "<string>",
      "created_at": "<string>",
      "description": "<string>",
      "metadata": "<string>",
      "labels": {},
      "tunnels": [
        {
          "id": "<string>",
          "uri": "<string>"
        }
      ]
    }
  ],
  "uri": "<string>",
  "next_page_uri": "<string>"
}