The NSW Office of State Revenue has released stamp duty data for September, with annual revenue falling 7% from May’s peak to $10.1 billion:

Down 7% over four months.
The decline in stamp duty follows the sharp fall in Sydney house prices since the Reserve Bank of Australia (RBA) first lifted the official cash rate (OCR) in early May:

Sydney dwelling values have fallen nearly 10% from peak.
Annual property transfers have also fallen sharply, down 13% from February’s peak:

Sydney property transfers tanking.
The next chart shows the annual change in transfers and stamp duties together:

Stamp duty receipts versus transfers falling fast.
The above stamp duty data lags house prices since it captures settlements, which typically occur 30 to 90 days after purchase. Therefore, the past several months of rate hikes would not be captured.
Given this inherent lag, and the fact that the RBA will likely hike rates further, house prices, transfers and ergo stamp duty receipts should continue to fall.