How to add ads between posts

hello Alx
How can I add google ads between posts in posts page, i found this code

php
if ( have_posts() ) :
  $counter = 1; //initialize the counter
  while ( have_posts() ) : the_post();
    if ( $counter % 4 == 0 ):
        // your ad code here
    else:
       get_template_part( 'content', get_post_format() );
    endif;

    $counter++; //increment by 1
  endwhile;
...
endif;
?>

Code link
https://docs.gaslamp.media/insert-ad-posts-wordpress/

I tried with this code over and over but it didn’t work with the typecore theme
do you have any idea to make this code work or any code?
thanks for theme

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