Plugin doesn't seem to be working…

I just installed and activated the code prettify plugin on my forums, but the plugin doesn’t seem to catch either the

<pre> or <code> front end flags. Here is how I’m formatting my text – is this the proper way to exercise the plugin?

Test Post
<pre>
test 123
test 321
</pre>
And... <code>Inline code</code>

If that is correct, what can I do to troubleshoot as to why the plugin is not working?
https://ww.wp.xz.cn/plugins/code-prettify/