在自定义帖子类型中添加自定义分类

I have registered a custom taxonomy it works fine and I also got the taxonomy list, but when I add this taxonomy in custom post it's not being added.

This code shows all of the custom taxonomy list:

 <?php $promotion_categories = get_terms('at_promotion_categories',array( 'hide_empty' => 0 )); ?>
     <select name="promotion_categories" id="promotion_categories" class="required">
    <option value=""><?php _e('Select Promotions Categories');?></option>
    <?php foreach($promotion_categories as $promtion_cat ):?>
    <option value="<?php _e($promtion_cat->term_id);?>"><?php _e($promtion_cat->name);?></option>
    <?php endforeach;?>

In adding post not adding this taxonomy in post, using the code below:

 wp_set_post_terms($post_id,array($promotion_categories_id),'at_promotion_categories');