working with EWS webservice

Question

the server is working, and I copied the code from MSDN

https://learn.microsoft.com/en-us/exchange/client-developer/exchange-web-services/how-to-authenticate-an-ews-application-by-using-oauth#add-an-authentication-token-to-ews-requests

But the response is "The request failed. The remote server returned an error: (403) Forbidden."