In Email Hippo WHOIS a domain name has expired but doesn't appear available for purchase. How can I buy it?

This article explains how to purchase the domain when it becomes available after it has expired.

When domain names expire they are sometimes temporarily deleted, in which case they are not available for purchase for some time after their expiration date.

It is in your best interest to use a drop catching service to ensure you are first in line to purchase the domain once it becomes available, and register it with an ICANN accredited registrar.