@akshaybhujbale
1. Assets API are like /api/assets/some_asset.json. Your endpoint is a request for a DAM resource straight forward. Assets API url for you would look something like:
https://author-p*****-e******.adobeaemcloud.com/api/assets/bcbsnc/pdf/providers/policies-guidelines-...
Please try and let me know if it works.
2. Maybe you have some rules in place ? https://experienceleague.adobe.com/en/docs/experience-manager-cloud-service/content/security/traffic.... Please be aware that AEMaaCS uses a CDN for author tier as well.