I can hit Dynamics API Endpoint (not 365) when I'm logged into Dynamics through browser. However, I can't use Postman to hit the same API endpoint. How can I use Postman using OAuth2 or other methods to hit the API?
There is a Microsoft Docs page with the instructions on how to use Postman for the Web API of Dataverse / Dynamics 365
https://learn.microsoft.com/en-us/power-apps/developer/data-platform/webapi/use-postman-web-api
Eventually you can build the requests using my tool Dataverse REST Builder, after you can export them as a Postman collection (the structure of variables is a bit different from the Microsoft documentation), the tool supports the Grant Type implicit (the one used my Microsoft in the documentation) or the Grant Type Client Credentials