NSW unpaid invoice: should I send a letter of demand before court?

Often, yes. The NSW Small Business Commissioner says a letter of demand can state the amount owed, the payment deadline and that further recovery action may follow if payment is not made. It can also show that you tried to recover the debt before going to court. Negotiation or mediation may still be worth trying because court can be costly and time-consuming. Official source: NSW Small Business Commissioner. Guide: https://getinstantlaw.com/small-business/customer-wont-pay-invoice