<?php $terms = get_the_terms( $main_post_id, 'category' ); ?> <?php foreach( $terms as $term ): ?> <a href="<?php echo get_term_link($term->slug, 'category'); ?>" class="catg-title"><?php echo $term->name; ?></a> <?php endforeach; ?>
Or Just do this
<?php echo get_the_term_list( $main_post_id, 'category', '', ', ' ); ?>