Per our API docs, the required Okta API Scope for this endpoint is okta.orgs.read. If you did follow the above guide to set up a Service App, have you granted this scope to said application and then requested this scope when you requested an Access Token from Okta?
I will note that the okta.orgs.read and okta.orgs.manage scopes are currently unavailable to enable within the Admin UI, so if your API Service app is not currently allowed to use this scope, you will need to enable it. Here’s the request you’ll need to complete: Grant consent to scope | Application Grants API | Okta Developer
Ah, this is for an OIN API Service Application? Based on what I see in your screenshot, it doesn’t look like this integration is allowed to use the okta.orgs.manage scope.
Is this for an existing OIN integration, or are you working on creating and submitting an integration to our OIN?