Atlas endpoint "Resource not found" via Purview API

Following this guide https://learn.microsoft.com/en-us/azure/purview/tutorial-atlas-2-2-apis I am trying to send any request to the atlas endpoint of my purview account (i.e. POST {{endpoint}}/api/atlas/v2/types/typedefs) or even just accessing the endpoint directly but the only response I get is: {"error":{"code":"ResourceNotFound","message":"Resource not found"}}.

I presume it is a problem with permissions but I have admin access to the subscription, resource group, purview account as well as all of the roles in the purview catalog (Collection admins_,_ Data source admins_,_ Data curators_,_ Data readers_,_ Insights readers_,_ Policy authors_,_ Workflow admins).

Can anyone suggest what could be configured incorrectly to not allow me to access the atlas endpoint?

I have reproduced the issue at my environment by referring this github link and got the expected result

I have followed the below steps-

1. I have done an app registration in Azure AD and created secrets too, to generate token. Grant the below permission as well. Refer SO question by @Vincent Diallo-Nort to know about how to grant permission.

2. Go to root collection as shown below

Provide permission to the app which you have registered in Azure AD as I have done below in collections. You can give permission to all the roles.

3. Generate token in postman using https://login.microsoft.com/<your tenant_id>/oauth2/token

4. Used the Bearer token to request URL https://afreen.purview.azure.com/catalog/api/atlas/v2/types/typedefs and got the result.