zingFit supports two modes for giving out a complimentary series. Both of these methods require that one series goes into the customer account before they can receive the free one.
Complimentary series can be activated by either purchase or usage.
Purchase: Once a series is purchased the complimentary one is put into the customer account.
Usage: Once the customer has used every credit in their series they will receive the complimentary one. The Customer will not receive the complimentary series if their series expires for any reason other than "series count".
To access complimentary series mode please navigate to Admin > Scheduling/Retail > Series/Contract > Edit or create a new series > Purchase Options/Restrictions > Complimentary series mode