Please go to Yammer applications page https://www.yammer.com/client_applications (you need to already have logged in your Yammer account)in the Register New App form. Then in the line 22 set the client_id to Client ID and client_secret with Client Secret. The Callback URL must be https://erp.leaf.com.my/webmail/modules/OAuthIntegratorWebclient/Classes/OAuthClient/login_with_yammer.php