Subscriptions are always based on a time and material project, and they can be created from a project, from the form, or by using a service subscription group.
For each subscription you can create an optional number of subscription fees. The subscription fees are the transactions that you invoice to the customer.
A period code indicates the extent of the subscription fee period, or the intervals at which the subscription should be invoiced.
The period code is defined in the service subscription group, and through the service subscription group it is defined for the subscriptions. Any new subscription fee that you create has a suggested start date, which is the start date of the period (if this is the first period created) or the end of the previous period (if this is the second or later period).