If you charge GST to a GST-registered customer, you need a full tax invoice unless the total including GST is S$1,000 or less. This guide lists the IRAS fields, the threshold, and a worked example.
A GST-registered seller must issue a tax invoice on request for taxable sales above A$82.50 including GST. This guide lists the fields the ATO expects and the A$1,000 buyer rule.
