i tried to have access to the instagram graph api but when i try to access the /media node of my account via the graph explorer tool i get "message": "(#100) Tried accessing nonexisting field (media) on node type (Page)",
Is it mandatory to send the screencast also to test the api?
No, you don't require to send screencast for Graph Explorer. You have probably missed setting up the Instagram business account. You can access the media node only via the instagram_business_account id that you get.
Here is the overview how you can set it up : https://developers.facebook.com/docs/instagram-api/getting-started/
And incase you're facing error fetching the instagram_business_account id after following the documentation here is a way to resolve it :