curl https://api.goshippo.com/carrier_accounts?service_levels=true \
 -H "Authorization: ShippoToken <API_TOKEN>"

{
  "next": "baseurl?page=3&results=10",
  "previous": "baseurl?page=1&results=10",
  "results": [
    {
      "account_id": "****",
      "carrier": "usps",
      "active": true,
      "parameters": {},
      "carrier_name": "USPS",
      "is_shippo_account": false,
      "metadata": "<string>",
      "object_id": "6aa34d5f6865448fbb1ee93636e98999",
      "object_owner": "bob+22@gmail.com",
      "service_levels": [
        {
          "name": "Priority Mail Express",
          "token": "usps_priority_express",
          "supports_return_labels": true
        }
      ],
      "test": false,
      "object_info": {
        "authentication": {},
        "verification": {}
      }
    }
  ]
}