2000 zip code taking me to Mexico instead Sydney

You can use the Append feature if all your locations are in Australia. This would require the experience add-on.
There have been various posts about this and how Google algorithms works. They are supposed to locate under the map domain you are using but Australia seems to have duplicate postal codes.

https://docs.storelocatorplus.com/wp-admin/post.php?post=858&action=edit
I have a test map for Australia and I use the Append shortcode on that map page. You might also want to change the center map at settings and radius settings.

See documentation for shortcode information
https://docs.storelocatorplus.com/blog/layout-shortcode-cheat-sheet/