How to use a token from one First-Party app to Auth. to a different First-party app?

Some background:

I have successfully set up SSO via Auth0 Universal Login in one of my apps.

I am attempting to submit that auth. token to a different first-party auth0 app which I have defined as an API.

Based on my understanding of Auth0, this should be possible, but I haven’t found anything in the docs.

Any ideas would be greatly appreciated!