N-Genius付款网关集成错误

如何解决N-Genius付款网关集成错误

这是用于获取我正在使用的访问令牌的代码，但得到的响应为“不可访问” 帮我解决这个问题

var client = new RestClient("https://api-gateway.sandBox.ngenius-payments.com/identity/auth/access-token");
            var request = new RestRequest(Method.POST);
            request.AddHeader("accept","application/vnd.ni-identity.v1+json");
            request.AddHeader("Authorization","Basic "+ Apikey);
            request.AddHeader("Content-Type","application/vnd.ni-identity.v1+json");
            request.AddParameter("application/vnd.ni-identity.v1+json","{\"realmName\":\"ni\"}",ParameterType.RequestBody);