If a taxpayer finds a mistake made on a previous activity statement, they can:-
The benefit of correcting a GST error on a later activity statement (where the conditions are met) is that the taxpayer will not be liable for any penalties or general interest charge (GIC) for that error. The ATO says it is generally easier to correct a GST error on a later activity statement than to revise an earlier activity statement. Revising an earlier activity statement that contains an error can incur penalties or GIC.
Accountants often prefer to amend the activity statement, to match the returns better with the accounting records, particularly if that results in an extra refund.