Once you've created a customer, you must create a billing group for them. If a customer has one contract, they will have only one group. If you have different contracts for the same customer, the lists will be grouped under the different contract plans.
1. Go to Utilities: Administration: Billing: Customers: Configure.
2. Click on Groups in a customer's row.
3. Click the Create New Group button.
4. Give the Group a Name.
5. Click Save.