Call Lookup API Gen3 retrieved 401 Unauthorized

Summary:

I am trying to call the following API to retrieve lookup data:

GET /ic/api/integration/v1/lookups/{lookup_name}

However, the request returns the following error:

{
"code": "NotAuthenticated",
"message": "The required information to complete authentication was not provided or was incorrect."
}

I need the detailed steps to generate the access token that should be used to successfully call this API?