I want to insert an ad generated by the adrotate plugin, I want to insert it after the third post in the list of a specific category, take the following code as an example and I wanted to change it but it does not work for me.

//Insert ads after second paragraph of single post content.

add_filter( 'the_content', 'prefix_insert_post_ads' );

function prefix_insert_post_ads( $content ) {

    $adrotate = adrotate_ad(3);

    $ad_code = $adrotate;
    //*ORIGINAL CODE
    /*if ( is_single() && ! is_admin() ) {
        return prefix_insert_after_paragraph( $ad_code, 2, $content );
   }*/
    if ( is_category('Financial') && ! is_admin() ) {
        return prefix_insert_after_paragraph( $ad_code, 2, $content );
    }

    return $content;
}

function prefix_insert_after_paragraph( $insertion, $paragraph_id, $content ) {
    //*ORIGINAL CODE
    //$closing_p = '</p>';
    $closing_p = '</article>';
    $paragraphs = explode( $closing_p, $content );
    foreach ($paragraphs as $index => $paragraph) {

    if ( trim( $paragraph ) ) {
        $paragraphs[$index] .= $closing_p;
    }

    if ( $paragraph_id == $index + 1 ) {
        $paragraphs[$index] .= $insertion;
    }
}

return implode( '', $paragraphs );
}

I appreciate your help

Read more here: How to Insert Ads within list post Category in WordPress