using RestSharp;


var options = new RestClientOptions("https://api.sandbox.{id}.gr4vy.app/payment-services/verify");
var client = new RestClient(options);
var request = new RestRequest("");
request.AddHeader("Authorization", "Bearer <token>");
request.AddJsonBody("{\n  \"payment_service_definition_id\": \"stripe-card\",\n  \"fields\": [\n    {\n      \"key\": \"private_key\",\n      \"value\": \"sk_test_26PHem9AhJZvU623DfE1x4sd\"\n    }\n  ]\n}", false);
var response = await client.PostAsync(request);

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

{
  "type": "error",
  "code": "bad_request",
  "status": 400,
  "message": "Missing '****' field",
  "details": [
    {
      "location": "body",
      "type": "value_error.missing",
      "pointer": "/payment_method/number",
      "message": "field required"
    }
  ]
}