This is probably due to the model's size. By default, 'Subsurface' value is set to 0.02 (in this material), which works fine for a 2x2 meters model. If your model is notably smaller than that, then you can either lower the 'Subsurface' value or scale up your model.

Make sure displacement is not disabled for your object. To check this, find the 'Displacement' value under the 'Settings' dropdown menu in your material settings tab, and switch it to either 'Displacement only' or 'Displacement and Bump'.

If the problem persists, then your mesh is probably not dense enough. You can fix this by adding a 'Subdivision Surface' modifier to your object and raise the amount of subdivision levels.