I created a private app (it has every permission and all possible read/write scopes).
All the Shopify REST APIs work fine. I have tested, prices rules, orders, customers, and others.
I run into a problem when I do a discount lookup call:
If I do this call with a non-existent discount code, I get a response
"errors": "Not Found"
"errors": "[API] Invalid API key or access token (unrecognized login or wrong password)"