Function as snippet?

I have this shortcode in my functions.php file

add_shortcode( 'buy_status', 'wpse249289_buy_status' );
function wpse249289_buy_status( $atts ) {
    $output = '';
    if ( ! get_post_meta( get_the_ID(), 'buy_status', true ) ) {
        // Post meta value for key buy_status is false
        $output .= '<h5 style="text-align: center;display: block;">';
        $output .= 'Sorry, this piece is sold.';
        $output .= '</h5>';
    } else {
        // Post meta value for key buy_status is not false
        $output .= '<h5 style="text-align: center;display: none;"></h5>'; // Not sure why you'd want to output anything
    }

    return $output;
}

I would like to put it in Post Snippets and call it from there. I’ve tinkered with doing that but can’t get it to work.

How would I put the code in Post Snippets? I assume the shortcode and php checkboxes would be checked?

Thanks!