Effective September 3 2021, the United States Postal Service suspended some international mail acceptance to Australia until further notice due to unavailable transportation. Merchants are asked to refrain from mailing the following services to Australia until further notice:

• Priority Mail International (PMI) – effective September 17
• First-Class Package International Service (FCPIS) – suspended September 3
• Commercial ePacket (CeP) – suspended September 3
• International Priority Airmail (IPA) Packets – suspended September 3
• International Surface Air Lift (ISAL) Packets – suspended September 3
• USPS Priority Mail Express International to Australia will be the only unaffected service available as of September 17

Error in the admin when purchasing the shipping label only applies to Australian addresses.

As of September 3rd, USPS has suspended most of their services to Australia because of reasons related to the pandemic.

You can read more about this here: https://www.eseller365.com/usps-suspends-package-services-to-australia/