Zoho Projects API Functional Example in C#

Zoho Projects API Functional Example in C#

I'm trying to use the manuals, but i have the error below:
  2. {
  3.     "error": {
  4.         "code": 6891,
  5.         "message": "Given URL is wrong"
  6.     }
  7. }

Url: https://projectsapi.zoho.com/restapi/portals
Header: "Authorization": "bearer token"

Can someone help me with this?
Thanks in advance.