Hi Oscprofessional,
thank you so much for your reply. Unfortunately this does not solve the error. The configuration just allows to change the normal acces scope for an app, created by the shop owner. But even then those are normal access scopes. The error message does not hint to the lack of a normal access scope. It says
The shop must have access to checkout server extensions.
and none of the APIs be it Admin or Storefront has this particular access.
Thank you so much,
Hagen