How to make WP understand functions outside the template, for example on the my_site.ru/dir/page.php page (for connecting via SSI in NGINX)?

Question

Nginx

Set up caching, everything works fine, enabled ssi.
At the root, WP created an ssi folder, page.php in it.
I insert it into the template so that part of the content on the page is not cached.
This also works, tested

echotime();

.
I inserted a part of the code from the template that I don't want to cache, and it doesn't output anything, it gives an error:

"PHP message: PHP Fatal error: Uncaught Error: Call to undefined function is_user_logged_in()

What can be done? Maybe there are other ways to "highlight" dynamic objects on the page that should not be cached?

Answer 1

PHP Fatal error: Uncaught Error: Call to undefined function is_user_logged_in()

Can you translate it yourself or can you do it yourself with the help of Google Translate?