you can use jwt.io to decode the access token.
please refer to https://experienceleaguecommunities.adobe.com/t5/adobe-experience-manager/verify-jwt-token-registered-oauth-clients/m-p/422055 and https://medium.com/tech-learnings/how-to-manage-the-protected-aem-resources-through-oauth-2-0-851ce4c7a5ef...