There are a couple of different reasons. For example:

• The address is in a remote location
• The address is incorrect

Here are some things you can do to try and resolve the issue:

• Check that the address is typed correctly.
• Try using an alternative address (like a business address versus a home address or vice-versa).
• Determine if the postcode recently split or changed. Changes to the population and mailing volume can result in new or reassigned postcodes, and it's possible our systems have not synced yet. If a change has recently taken place, try using the "old" postcode