The postal code is a 7-digit numeric code allocated to each area to facilitate the sorting and categorization of the postal items.
On the other hand, the Digital Address (JPN ver only) is a new service that can define your entire home address in a 7-digit alphanumeric code.
<Japan Post Web Page Postal codes and barcodes manual (postal code)>
https://www.post.japanpost.jp/zipcode/zipmanual/p04.html