Error code 0x80131500 when using Rest Api

[project101]

For Api calling with  c#  to get tokem number or report

var credentials = new TokenCredentials(vars.Azure.accessToken);

client.BaseUri = new Uri("https://api.powerbi.com");
var generateTokenRequestParameters = new GenerateTokenRequest(accessLevel: "view");
var r= await client2.Reports.GenerateTokenInGroupAsync(vars.ApiBi.groupBi, vars.ApiBi.reportBi, generateTokenRequestParameters);

here is the error 

System.AggregateException HResult=0x80131500
Inner Exception 1:HttpOperationException: Operation returned an invalid status code 'NotFound'

i have pro version for power bi and free version for azure 

using c# 2017-2019