How to get Queryable objects using GraphQL Admin API?

Hmm, I think I am looking at Graphql Admin API as my endpoint and header settings are below.

https://{shop}.myshopify.com/admin/api/2019-10/graphql.json

Content-Type: application/json

X-Shopify-Access-Token: <ACCESS_TOKEN>

But I got an error says:
“Internal error. Looks like something went wrong on our end.\nRequest ID: dc665f52-1f95-4451-8a16-1d6a40ed2d39 (include this in support requests).”