‘Nudges’ have increased tax revenue in settings with high rates of compliance and effective enforcement, but can they work in countries that lack these conditions? The study tests this through a population-wide randomised control trial of Small and Medium Sized Enterprises (SMEs) in Papua New Guinea — a setting where no one has faced criminal charges for non-compliance and where 95 per cent of registered SMEs do not make the required monthly Salaries and Wages Tax (SWT) lodgements. The sudy tests the effectiveness of SMS messages that either remind SMEs of lodgement due dates or inform them about the public benefits from paying tax. Both treatments doubled on-time SWT lodgements by SMEs with no employees. However, this did not increase revenue, as sole-traders are exempt from paying SWT. These findings support seminal theories that propose taxpayers who face the lowest cost from complying are the most likely to respond to a nudge.