[Writing a shortcode function for Wordpress]

Hello- I am not generating any errors with this php snippet which is in my functions.php file of the child theme for wordpress but I'm wondering why it doesn't work.

Snippet:

function pnavi_shortcode() {
return get_the_post_navigation();
}add_shortcode
    ( 'pnavi', 'pnavi_shortcode' );

I have also tried using a variable = to the function of get_the_post_navigation() but same issue. This script is supposed to show the previous - next navigation for pages of posts, not the 'next' single post.

Via a theme, it is working, but I'm trying to add something myself in another location. Any suggestions?