Send the Invoice as Base64 String

var options = new RestClientOptions("https://apitest.nilvera.com")
{
  MaxTimeout = -1,
};
var client = new RestClient(options);
var request = new RestRequest("/einvoice/Send/Base64String", Method.Post);
request.AddHeader("Content-Type", "application/json");
request.AddHeader("Authorization", "Bearer <API KEY>");
var body = @"{"ZIPFileBase64": "string",
"Alias": "urn:mail:defaultpk@furkantatlisu.com"}";
request.AddStringBody(body, DataFormat.Json);
RestResponse response = await client.ExecuteAsync(request);
Console.WriteLine(response.Content);