Can you add more information on the error you are getting. Namely

1) the HTTP response status code
2) the HTTP response body (if any)

Hi Teguh

Did you use:
POST /v1/session?_method=delete
or
GET /v1/session?_method=delete

Thx
~jimmi

1. You must use Method: DELETE
2. You must specify session id in your request uri: /v1/session?sid=sessionId

You can build the request URL as follows:

string url = "http://developer.messenger.yahooapis.com/v1/session" +
"?oauth_consumer_key=" + consumerKey +
"&oauth_nonce=" + new Random().Next(123400, 9999999).ToString() +
"&oauth_signature=" + consumerSecret + "%26" + oauthTokenSecret +
"&oauth_signature_method=PLAINTEXT" +
"&oauth_timestamp=" + getTimestamp() +
"&oauth_token=" + oauthToken +
"&oauth_version=1.0" +
"&notifyServerToken=1" +
"&sid=" + yahooSessionInfo.sessionId;

HttpWebRequest logoffRequest = WebRequest.Create(url) as HttpWebRequest;

logoffRequest.Method = "DELETE";

And once you make the request, you will be logged off. I think Yahoo doesn't send back any response text, just a status 200 OK.