As at the time of writing this article, the present licensing model for ODT Rentals is usage based.  This is tracked by the Rental Invoices that are posted.  Regardless of your agreement and whether you pay as a monthly fee or transaction based, ODT must create a license key to add a quantity to continue processing rental invoice transactions.

When viewing the License Info, you can determine the Licensed Transactions and the Current count.  Prior to reaching the maximum it is advisable to contact ODT ahead to arrange for another license key.  You can edit the license warning to notify ahead of using all available.

Use the Enter License Code option to enter the code provided by ODT.