Okta SSO 401 Unauthorized Error

Firstly, I am pretty new to SSO.
I want to integrate single sign on in my angular 6 web application with spring boot 1.5 backend.

I am able to successfully integrate the OKTA with my angular 6 application and has also enabled oauth2, resource server in the backend.

Now, After successful login, okta redirects me to my application home page and I am passing the OKTA access token to my backend url and I am receiving 401 unauthorized error. Can anyone suggest how to resolve this, or am I missing something here ?

How can I use the OKTA access token received in my front end angular app and make sure I can access my java backend with spring boot 1.5 ??

Thanks in advance.