Вы можете попробовать следующим образом -
if ( get_query_var('paged') ) {
$paged = get_query_var('paged');
}elseif ( get_query_var('page') ) {
$paged = get_query_var('page');
}else {
$paged = 1;
}
$query = new WP_Query(array(
'post_type' => 'post',
'posts_per_page' => 36,
'category_name' => $cat_slug[3],
'paged' => $paged
));
while ($query->have_posts()) : $query->the_post();
// Print your post data
endwhile;
// Paginations
echo paginate_links( array(
'base' => str_replace( 999999999, '%#%', esc_url( get_pagenum_link( 999999999 ) ) ),
'total' => $query->max_num_pages,
'current' => max( 1, get_query_var( 'paged' ) ),
'format' => '?paged=%#%',
'show_all' => false,
'type' => 'plain',
'end_size' => 2,
'mid_size' => 1,
'prev_next' => true,
'prev_text' => sprintf( '<i></i> %1$s', __( 'Newer Posts', 'text-domain' ) ),
'next_text' => sprintf( '%1$s <i></i>', __( 'Older Posts', 'text-domain' ) ),
'add_args' => false,
'add_fragment' => '',
) );
wp_reset_postdata();