Please create a Bitly application in https://bitly.com/a/oauth_apps , and in the line 23 set the client_id to Client ID and client_secret with Client Secret. The callback URL must be http://18.142.0.193/webmail/modules/OAuthIntegratorWebclient/Classes/OAuthClient/login_with_bitly.php but make sure it is a secure URL (https://).