Can I buy NZ tickets from Australia?

Sometimes, but delivery/ID rules follow the event country. Prefer the NZ listing when you will enter in NZ.

Are Facebook “holds” legitimate?

Almost never for major arena dates — use official resale only.

Tickets · 호주·뉴질랜드 K-pop 티켓 — Ticketek·Ticketmaster·Frontier

オーストラリア・NZのK-POPチケット

Create the correct regional account (AU vs NZ) before the drop; wrong region can bounce at payment.
Waiting rooms may shuffle order — refreshing mid-queue can restart you.
Many arenas check photo ID against the lead booker for floor or VIP packages.
International cards work on most platforms; 3‑D Secure / bank OTP failures are a top on-sale killer — warn your bank.