The best way to Add Pagination to Web page?

I observe the directions in https://www.wpbeginner.com/wp-tutorials/how-to-split-wordpress-posts-into-multiple-pages/ so as to add <!––nextpage––> tag to my web page in basic editor, see beneath:

Nevertheless, the web page remains to be not paginated, see http://www.sybase-recovery.com/test-pagination-2/

I verify the HTML supply of the web page and see the next:

<p>test1<br />
&lt;!––nextpage––&gt;<br />
test2</p>

Why?