Low participation rates can be influenced by many factors. We would firstly recommend using the sharing features to promote your study. However, very specific requirements will often mean that you are trying to reach a small percentage of the population which can be challenging, we would recommend forwarding your study page to specific charities.
Low compensation or voluntary studies are less attractive than those who pay. If you are unable to offer any competitive compensation you could consider partnering with a local charity or company, additionally talk to your employer or institutional communications department who may be able to promote your study page.