Australia Post has declared this issue resolved

Hi All,

Startrack has updated advising that they have implemented a fix but are still monitoring

Errors may still appear but MachShip can advise that you can look to create and manifest consignments with Startrack / Australia Post

We will continue to update as information becomes availablele

Australia Post has acknowledged the issue with their system and is investigating

They are advising on the ticket below:
https://status.developers.auspost.com.au/incidents/gf0d8jmhh0xt

Currently, the Shipping and Tracking API is experiencing errors when pricing and booking

MachShip has lodged a ticket and will advise as information becomes available