We want an existing card to be automatically marked as the default during a new subscription purchase

🔍 Problem Statement

When a customer adds a new credit card during a subscription update, the new card is not automatically set as the default payment method. The old card remains the default, which can cause failed renewals if the old card is expired or revoked.

💡 User Story

As a subscriber, I want my newly added card to automatically become the default payment method, so that future renewals use the most recent card without a separate manual step.

🎯 Definition of Done (DoD)

A feature is done when:

✔️ Given a customer who adds a new credit card during a subscription flow, when the card is saved successfully, then it is automatically marked as the default payment method for the account.