Custom post type category not displaying category ID

get_the_category retrieve array of post categories.

This tag may be used outside the loop by passing a post id as the parameter.

The syntax is

$categories = get_the_category(  $post_id  ); // Outside the loop

// OR

$categories = get_the_category( ); // Inside the loop

Note: This function only returns results from the default “category” taxonomy. For custom taxonomies use get_the_terms() .

$categories = get_the_terms( $post_id, 'taxonomy' );

I hope this may help.