The new Cashier 9.3 release comes with two changes you might want to take into in account when upgrading.
First, card failures for new subscriptions are handled differently. Cashier will now throw a custom exception instead of the Stripe Card exception.
Additionally, a bug was also fixed when dealing with card failures during plan swapping. This change requires the implementation of webhooks to handle the related Stripe events.
More information on these two changes can be found in the upgrade guide.
We also want to stress that webhooks are becoming increasingly important when working with Stripe, and we recommend that you always configure them when using Cashier.
Meanwhile, we've begun development on the next major version for Cashier, v10. This release will contain some of the most significant changes to Cashier to date with support for the new Payment Intents API and potentially Stripe's new Checkout product. These changes are needed to comply with the new SCA regulations that begin during September. You may follow along with the development of Cashier v10 through its milestone. Please note that the issues listed aren't necessarily going to be in the final release. A thorough upgrade guide and updated documentation will be provided when Cashier v10 is released.