Given a registered customer with a bank account And a registered merchant with a bank account And the customer has 0 unused token And the customer has 1 used token And the customer has 100 kr. in the account And the merchant has 0 kr. in the account When the merchant scans the used token for 100 kr. Then an error will occur saying "Invalid token" And the customer will still have 0 unused token left And the customer will still have 1 used token And the customer will still have 100 kr. in the account And the merchant will still have 0 kr. in the account