Authentication failing / Out-of-date documentation

While following along with the example project found on the React with GraphQL page, it details a process called Introspection Fragment matching with GraphQL.
My first question is, is this file necessary/does it bring any benefit to the project?

I ask because both the sample project and the Introspection fragment matching page I linked above seem to both be out-of-date and using the old version 1 API.
As my repo is private I also need to adjust the sample given, in order to attach some headers to the fetch request..
I have tried following the sample given on this page - Introduction To The Content Query API to test using an access token and it has not worked. To quote the page

The Access Token

If you've set your repository to private, then you'll need to provide an access token in order to retrieve your content. To do this you will need to use the access_token parameter and provide your token.${MY_ACCESS_TOKEN}

This does not work, I receive a 403 Forbidden. I also tried with replacing the Your_ref with "master", (even though this is not documented) to no success.

I have also tried following the example in the following page - Intro to the GraphQL API.

Supposedly all you need to do is query the endpoint with a "Authorization" header and a "Prismic-Ref" header. I receive a 'Invalid access token' error.

And just to be clear, I only have a single permanent access token which I have been using when required.
Any help is appreciated. Thanks for reading!