You are not criminally responsible for a strict liability offence in New South Wales if you establish on the balance of probabilities that you were honestly mistaken about a fact essential to proving the offence, and your belief was reasonable in the circumstances.
A strict liability offence is one where the prosecution does not need to prove a mental element, such as intent, recklessness or negligence.
The defence of honest and reasonable mistake does not excuse ignorance of the law, but relates to your understanding of the facts of your situation.
The test for whether your mistake was honest relates to your own belief at the time, while the test for whether it was reasonable assesses whether a reasonable person in your situation would have held the same belief.