Order expires after 1 day although it is completed

Hello,

this time I have an issue I am not sure about if it is my mistake anyhow or a bug. When someone orders pixels and does not pay but I confirm the order and complete it in the admin area (because he gets the pixels for free) and also process the pixels, everything is fine. They are there and i can see it under "order: completed" in the admin area. But the problem is that the order somehow expires after 24 hours (the user can also see it in his account that it expires in the certain amount of hours) - and the pixels are gone. In the admin area I can then see the order under "Orders: Expired" and can again complete it and so on - but again it only works for 24 hours...

You think that there is something I could do about this?

Thank you so much in advance!!!

Regards

Lukas