To use this module, you need to:

1.  Create an Account Invoice triggering at least one "Tier Definition".
2.  Click on Request Validation button.
3.  Under the tab Reviews have a look to pending reviews and their
    statuses.
4.  Once all reviews are validated click on Post.

Additional features:

- You can filter the Account Invoices requesting your review through the
  filter Needs my Review.
- User with rights to confirm the Account Invoice (validate all tiers
  that would be generated) can directly do the operation, this is, there
  is no need for her/him to request a validation.