Sometimes the carrier will determine that they are not able to deliver the package to the shipping address.  While we cannot be certain why for your specific situation,  it can range from a missing apartment number, to an address they have determined as "undeliverable".  The only way to be certain is to check directly with the carrier that left the undeliverable notice, as these situations are beyond our control.    

You can check online to see if the United States Postal Service (USPS) can re-deliver your package by going to:  https://tools.usps.com/redelivery.htm