ESRI suggest API returning incorrect result for Australian postal code.

[SHIVAM1995]

In one of our applications, we use ESRI suggest API to get suggestions against postal codes. However, we are getting incorrect responses for Australian postcodes. 
example we tried with postcode `3068`

we got suggestions like 

 "3068, Clifton Hill, Northcote, Melbourne, Victoria, AUS"

 "3068, Brunswick East, Fitzroy North, Melbourne, Victoria, AUS"

 which is incorrect.

[SHIVAM1995]

API used was
https://geocode.arcgis.com/arcgis/rest/services/World/GeocodeServer/suggest?text=3068 &f=json&token=XXXX&outFields=*&maxSuggestions=15&category=Address,Postal&countryCode=AU&returnCollections=true

[GrahamWood-HWC]

here is the definitive source for Australian postcodes
https://auspost.com.au/postcode 

3068 is Valid for both suburbs..

post codes in Australia have their history in the catchment area of a post office(back in the days of post) which may reach beyond suburb boundaries... my post code reaches across 9 suburbs