private async Task PostPayloadAsync(Payload payload)
 {
     using (var client = BuildHttpClient())
     {
         var data = JsonConvert.SerializeObject(payload);
         var response = await client.PostAsync(_uri, new StringContent(data, Encoding.UTF8, "application/json"));
     }
 }
        private Payload BuildPayload(string text, string username, string channel, IEnumerable<Attachment> attachments = null)
        {
            username = username ?? "";

            var payload = new Payload
            {
                Channel = channel,
                Username = username,
                Text = text,
                Attachments = attachments
            };

            return payload;
        }