If I understand
@Atleastonce's question correctly, the problem is I think they are wanting to add an internal domestic flight within the US to their itinerary, not a flight from the US back to Australia?
I have a similar issue in looking for flights for a holiday I'm taking to the US in 2025 (was 2024, but had to be delayed). I need to fly into Cody, Wyoming, but on the Velocity site can only get as far as Denver. Cody does not come up as a destination or able to be selected as a starting point. (as per
@bcworld's very helpful post below, this is for a revenue flight, not rewards).
I can book all the way to Cody through United, who are usually the only airline who fly in there for much - if not all - of the year, however I cannot book the same through the Velocity website, and booking the Denver-Cody return flights separately with United are hideously expensive, regardless of the time of year, as there's a very limited number of flights (2in/out each day) except for a couple of months in summer.