If you have received a message that your package has been returned to the sender, you need to get in touch with the sender. They are able to check and update your details, and get in contact with the carrier who is trying to deliver your parcel.
There are a broad range of reasons why a package might get returned to the sender:
The address the package was sent to does not exist or is incomplete
Someone at the address refused to accept the package
There is a problem with your package and the sender recalled the delivery
The driver attempted multiple times to deliver the package but wasn't able to
The driver couldn't access the address because of security restrictions, or the presence of animals
No one was at home, and the driver is unable to leave the package without a signature
Regardless of why your package was returned, get in touch with the sender to check your details, and get your package sent out again.