Unable to retrieve Ticket activities

Unable to retrieve Ticket activities

I have the following scope,

Desk.contacts.all,Desk.products.all,Desk.settings.all,Desk.basic.all,Desk.tickets.all,Desk.activities.calls.READ , Desk.activities.events.READ , Desk.activities.READ , Desk.activities.tasks.READ , Desk.calls.READ , Desk.tasks.READ , Desk.events.READ


 and I am trying to retrieve ticket activity via this url, https://desk.zoho.com/api/v1/tickets/ticketID/activities
but get the following error
Error: Unexpected response with status code 401