1st Step: Create a promotion

Check this article for a quick overview of the process: here

2nd Step: On the promotion settings, select the right option for the subscriptions as shown below, where you indicate to the system that the promotion will only last until the automatic renewal:

3rd Step: Create a subscription or adjust one previously created to have the period of time where you want the discount to be applied (if it's 6 months then this setting should be set to 6 as it's the period of time before the automatic renewal).

Check this article on how to create a subscription if needed.

Make sure to tick the option to automatically renew the subscription for the member to pay the full price after the initial time period with the discount has ended:

4th Step: Share the code of the promotion with your members and they'll be able to add it when purchasing a subscription:

You'll be able to add it yourself from the backoffice as well when billing a member: