Hello TriOmegaZero,
You attached the store credit to them. With sidecarts this is a little complicated though. When your subscription order is generated the system will reach into your sidecart and pull anything there that is ready to go into the order. When it does this it is going to ignore any payment options selected for the items in the sidecart and use the subscription payment method for the entire order. To use store credit for that order there are 2 things you can do. If you set your subscription to use your store credit it will apply the store credit to that order when it generates and only charge your card for the difference. The other is to let us know when you receive the order confirmation and we can manually apply your store credit to the order.
