To avoid breaching the contract: pay on or before the due date, either by cheque delivered directly to the deposit holder, or by electronic transfer with written evidence provided at the time of payment. Keep your own records and don't rely on payment instructions from the seller or agent that differ from what's in the contract. How much you need to pay, who holds it, and what specific rights the seller has if you're late all vary by state — see the state-specific detail for NSW, QLD and VIC.