‘Expired’ means that you have left your parcel in the box for too long. It is still safely in the box and has not been returned to the online shop, but you can no longer pick it up yourself.
Thankfully the Box Mayor can help you. Contact your Box Mayor. You can find their details on the dedicated web page for your box. They will take your expired parcel out of the box and place it in another compartment, at which point you will have a further five days to pick it up.