The Subscription Expired event is triggered in two situations:

• If the buyer fails to initiate or complete 3D Secure Authorization during the transaction process
• Or, if a new Subscription’s charge fails after a Subscription Change/Swap

This automation is best used to run maintenance actions (like removing access, etc) on Subscription purchases that weren’t successful.

Learn more about 3D Secure

This event can be set up Globally or at the Subscription Group level.
Learn more about Global Billing Automation & Subscription Group Billing Automation