On page 139 in the iex session in the Test Drive the Schema section, the instruction is to execute Product.changeset/2. However, the previous chapter set up scopes and authentication, so the function is changeset/3, requiring a scope. This is also reflected on p 136, where in the iex session, exports Product shows changeset/2 in the book, but changeset/3 for the user.
The function is correctly described on p 137 as including the user_scope.
A similar error testing the changset function is on p 140 of the same section.