Hello Mauricio Igor,
Thanks for reaching out, to resolve the "token validation failed" error, please try to refresh your authentication session. Open a private or incognito browser window and sign into the Azure portal again, which will generate a fresh security token. If the issue persists, ensure the Microsoft.EventGrid resource provider is registered in your subscription's "Resource providers" settings. Lastly, verify in "Access control (IAM)" that your account has the necessary permissions, such as the Contributor role, on the resource you are trying to monitor.