In the left menu, go to the Plans tab and click the "Create" button.
Fill in all the required fields. Almost every field will be given tips on how to do it.
More info on - https://github.com/slntopp/nocloud/wiki/Billing-Plans

Perform a connection test using the Test button at the very bottom of the page, and if the test is successful, we can create a tariff plan.

If you have created a Prepaid plan, then you can add more tariff plans already inside the newly created plan. Price and configuration can also be managed within the created plans.