oAuth2AccessTokenResponse error

[sabbouh]

Hi,
Im trying to use this application for test and i have an error for Token in OAuthHelpers.cs in line 82 with the code
var oAuth2AccessTokenResponse = ParseOAuth2AccessTokenResponse(responseString);
the message is :
ApiClient.Exception.ApiException: 'Error trying to refresh token. Invalid Request - Error(s) in Post Request field(s): refresh_token is null or undefined'
thank you for your help