The most common reason authors have this problem, is that you can't have a blank line between the sample directive, and the heading. So, this won't work:
{sample: true}
# Chapter One
...but this will:
{sample: true}
# Chapter One
The most common reason authors have this problem, is that you can't have a blank line between the sample directive, and the heading. So, this won't work:
{sample: true}
# Chapter One
...but this will:
{sample: true}
# Chapter One