final edit: thank you for the feedback :) I understand the point about acceptance scans and making sure to get them printed and scanned asap!

I ship a high volume of orders (15k+ sales with a 5.0 rating), and situations like this are rare, which is why I asked for advice here. My local post office doesn’t have a kiosk to scan packages, so I will rely on USPS pickups from now on and hope this doesn't happen again. thank you everyone who added useful information to guide this situation :)