problen to try to export report to CSV using api 3 in c#

Hello, i have a problem triying to export to file using api 3.0 in c#.

When i am using Client.Reports.GetPage(groupId, reportId, pageName) always return me "Error to send the request". what i am doing wrong.

The APP is well configured because I created the APP in azure (power bi Embedded) using the wizard, and download the sample project, after that i implemented the Api rest v3 (using the microsoft example) but always get the same error.

Client.Reports.GetPage(groupId, reportId, pageName)

i am trying to use this code,  but always get the same error . i have the token, the apiurl, the group id and report id. 

var tokenCredentials = new TokenCredentials(dm_token, "Bearer");
var Client = new PowerBIClient(new Uri(dm_ApiUrl), tokenCredentials);
Pages GetPage = Client.Reports.GetPagesInGroup(groupId,reportId );