Hi @oussbak16,
Welcome to the Community!
When an audience
is provided in the authorize request, then the Access Token will be a JWT that you can decode using a library such as the ones listed on https://jwt.io/.
If an audience
is not provided, then an opaque token will be returned to your app, which cannot be decoded.
For more information on this, you can take a look at this FAQ:
https://community.auth0.com/t/why-is-my-access-token-not-a-jwt-opaque-token/31028/4