SDK createCart with api key 403 error

Question:
SDK createCart seems to be not supported for use with api key. Created an account level api key with all permissions, but keep getting 403 on createCart. Tested same code with OAuth, works.

Product:
n/a

What are you trying to achieve:
Create/manage creation of cart, checkout and payment.

What have you already tried:
SDK & fetch, multiple websites, headless, not, premium etc.

Additional information:
Oauth seems to be the only valid way to get full control with the sdk. Other methods do seem to work like queryProducts or getProduct