Custom checkout

I'm doing a custom checkout through the MercadoPago API and sending this data returns the error:

transaction_amount attributte can´t be null.

var token = Authenticate();

var client = new RestClient(_restClient);

var request = new RestRequest("v1/payments", Method.POST);

request.AddParameter("access_token", token.access_token);
request.AddParameter("Public_key", Config.GetPublicKey(_mode));
request.AddParameter("currency_id", "ARS");
request.AddParameter("transaction_amount", 100);
request.AddParameter("description", "Compra nº 1");
request.AddParameter("installments", 1);
request.AddParameter("payment_method_id", "visa");

var response = client.Execute(request);