That suggests that the import script didn’t create an admin account. If you just log in and/or create an account using the developer_email address, you’ll be OK.
That’s likely because restoring the backup turned off email for non-staff and that user isn’t staff.
Maybe? It’s certainly a chicken-egg issue with a new site and a migration. I think if you add your user to developer_emails then it’ll work.
The other thing you can do is add something like this to your script:
User.create(username: 'pat-the-admin', email: 'pat@user.com',password: 'very-safe-123', active: true, name: "Pat User") unless User.find_by_email('pat@user.com`)