There is no obligation to purchase a .au direct domain for your third-level .au domain.
All non-registered (unallocated) .au direct domain names with priority hold status will be released to the general public for registration from 8:00 AM AEDT on Oct 04, 2022 on a ‘first-come, first-served’ basis. This is the date when the auDA registry will start processing the first completed application for .au direct domains.