Automatically adding unique advert number

Each ad has internally assigned ID, you can display it on Ad details page with following code

add_action( "adverts_tpl_single_details", "my_adverts_tpl_single_id" );

function my_adverts_tpl_single_id( $post_id ) {

    ?>

    <div class="adverts-grid-row">
        <div class="adverts-grid-col adverts-col-30">
            <span class="adverts-round-icon adverts-icon-wordpress"></span>
            <span class="adverts-row-title">ID</span>
        </div>
        <div class="adverts-grid-col adverts-col-65">
            <?php esc_html_e( $post_id ) ?>
        </div>
    </div>

    <?php

}

The code you can add in your theme functions.php.