Unauthorized 401 error when connecting to Dynamics CRM 365 OData using Postman

I Have a trial license for Dynamics 365 CRM online. I can connect from office 365 to the url of the Crm service in IE Explorer as:

        myorg.crm4.dynamics.com
The url is like this
Also I can access Odata as:

         myorg.crm4.dynamics.com/.../accounts

I try to connect to the Odata service using Postman.I created an application in azure with permissions to CRM as described here
I get an access_token, so this insure that the resource is valid.
I tried to do GET request to the resource using this valid access_token but postman respond with 401 Unauthorized
I read tens of pages but it can't help. I suspect (but not sure) that Odata service may not available in the trial version for developers.

The Question:
What I missed to run that example and connect to OData service?
Why I get the error Unauthorized 401 although i pass a valid access_token generated for the service myorg.crm4.dynamics.com