Trial feature

When a Trial is configured for a plan (Period & Unit), all the subscriptions created under this plan would have a trial period.
The start date of the subscription then represents the start date of the trial.
The trial end date would be calculated based on the trial Period & Unit provided (e.g 14 days).

Having the trial feature active for a specific subscription reflects on defining the next billing date.
If we are dealing with a pre-paid subscription, then the customer would be charged when the trial ends; the next billing date would be the trial end date.
Otherwise if the subscription is post-paid, then at the end of the trial we start the billing cycle and the customer would be charged at the end of this cycle.
This ensures that the subscriber in the post-paid scenario wouldn't be charged for the trial period.

During the creation of a subscription plan and to activate the Trial, simply pass the desired values in the parameters trialDurationPeriod & trialDurationUnit to specify a trial period for all subscriptions created under this plan.

The same could be applied by updating a plan and providing the new desired values on the same parameters: trialDurationPeriod & trialDurationUnit.
The new trial details would be applied then on subscriptions created under this plan going forward without impacting or changing the previously created subscriptions.

This is also applicable if the merchant wants to remove the trial details from a specific plan, you can simply update the trialDurationPeriod & trialDurationUnit parameters with "null" values, which means that future subscriptions created under this plan would have no trial period.