There are various factors as to why a parcel could be undelivered and end up getting returned or abandoned. Some of the top reasons are:
Insufficient/Incorrect address.
Ensure that your Customer Orders have a complete (and correct) address before placing the order on Blanka.
The parcel requires duties/taxes to be paid (for applicable countries) in order to clear customs.
Your customer did not include a phone number when they placed the order.
In this instance, the delivery courier may have attempted to deliver the parcel but did not find the address indicated on the order and was not able to contact the receiver due to a lack of contact number.
Tip: Ensure that your Customer Orders include a phone number before placing the order on Blanka. If your country privacy laws allow it, consider asking/requiring your customers to provide their phone number when placing an order on your store.