How to send a notification to the OneSignal API with flurl - .net-core

Question

I'm trying to send some data using the example in the page of onesignal
var request = WebRequest.Create("https://onesignal.com/api/v1/notifications") as HttpWebRequest;
request.KeepAlive = true;
request.Method = "POST";
request.ContentType = "application/json; charset=utf-8";
request.Headers.Add("authorization", "Basic xxx");
var obj = new
{
app_id = "xxx",
contents = new { en = "English Message" },
included_segments = new string[] { "Active Users" }
};
var param = JsonConvert.SerializeObject(obj);
byte[] byteArray = Encoding.UTF8.GetBytes(param);
This coded works fine, but I'm using Flurl to make a request to onesignal like this:
var body = new
{
app_id = "xxx",
contents = new
{
es = "Mensaje prueba"
},
included_segments = new string[] { "All" }
};
string param = JsonConvert.SerializeObject(body);
var content = new System.Net.Http.ByteArrayContent(Encoding.UTF8.GetBytes(param));
var response = await new Flurl.Url(urlbase)
.AppendPathSegment("notifications")
.WithHeader("Content-Type", "application/json; charset=utf-8")
.WithHeader("Authorization", "Basic xxx")
.PostAsync(content)
.ReceiveString();
but I'm getting the "Bad request". Please someone could help to point how to make the same call with Flurl?

Answer 1

As mentioned in the first comment, you're doing more work than you need to. Flurl will serialize body for you, so remove these lines:
string param = JsonConvert.SerializeObject(body);
var content = new System.Net.Http.ByteArrayContent(Encoding.UTF8.GetBytes(param));
And post body directly using PostJsonAsync:
var response = await urlbase
...
.PostJsonAsync(body)
.ReceiveString();