There is a problem with at least one scope element
Scope Owner doesn't have access to one of the elements (Board/ Filter/ Project) you have tried to use to define the Box scope.
Example
The app 'reads' all tasks through the lens of a Scope Owner. A Box can only include tasks to which the Scope owner has at least viewing access.
In the example below, "Tofu" is the Jira user chosen to be a scope owner. User "Tofu" doesn't have permission to access the project added to the scope definition. As a logged-in user, you can have full access to a given item, but if the Scope Owner can't access it, the error will pop up.
Solutions
Change the scope owner
You can use a different user as a scope owner. The new Scope Owner user must have permission to access a given project/filter/board.
Change permissions of the item
In the example above, the Project permissions were the problem. Go to project settings:
You have two options.
Associate a different scheme with the project.
Modify the existing permissions scheme.