using RestSharp;


var options = new RestClientOptions("https://api.sandbox.{id}.gr4vy.app/gift-cards/balances");
var client = new RestClient(options);
var request = new RestRequest("");
request.AddHeader("Authorization", "Bearer <token>");
request.AddJsonBody("{}", false);
var response = await client.PostAsync(request);

Console.WriteLine("{0}", response.Content);

{
  "items": [
    {
      "type": "gift-card",
      "id": "e6cdf979-87e2-4796-8ff6-9784d5aed893",
      "merchant_account_id": "default",
      "bin": "412345",
      "sub_bin": "554",
      "last4": "1234",
      "expiration_date": "2013-07-16T19:23:00.000+00:00",
      "balance": 1299,
      "currency": "USD",
      "balance_error_code": "incorrect_currency",
      "balance_raw_error_code": "10363",
      "balance_raw_error_message": "This currency is not supported by the merchant."
    }
  ]
}