What are the minimum details that must be included in a request for payment to be a valid financial document and enforceable debt in Australia?

For a tax invoice for sale of less than $1,000 the following seven details must be included:
1. That the document is intended to be a tax invoice. Usually done with the words "Tax Invoice" written in big bold letters at the top
2. Seller's identity i.e. name
3. Seller's ABN (Australian Business Number)
4. Date of invoice
5. Description of items sold
6. GST amount (if any) payable or a statement clearly stating if GST is not applicable or if total price includes GST
7. Extent to which each sale includes GST

Tax invoices for sale of over $1,000 must also include:
1. The buyers identity or ABN