not making a new page

I have a few long pages, and would like to make them into several pages with pagination. I use the advanced layout editor, so I inserted a code block with the <!–nextpage–> tag in the places I wanted to end each page. However when I go to the page, all that has happened is a page break (grey line) inserted across the page. Have I missed something, or what could the problem be?

Thanks in advance.