@Mathias Rönnlund When you create a new subscription, you can specify a new credit card. When you do so, no other subscriptions get associated with the new credit card. You can add multiple new subscriptions, each with a unique credit card. However, if you later make any of the following changes, all subscriptions will use the payment method you select.
- Make a payment method active with the Set active option
- Use the Replace payment option for any subscription
- Change the default payment method
Kindly note that this is by design. For more information, refer this document.