New Zealand → Fiji
New Zealand plugs
Type IFiji plugs
Type IShared plug type: I
Compatibility: Compatible
Voltage — New Zealand 230V — Fiji 240V
Voltage difference is small. Most electronics will work safely.
Device compatibility (phones)
Phones almost always support 100–240V, so yours should work safely. Check your charger label to confirm.
You likely only need a plug adapter (if socket shapes differ). Voltage is close between these countries.