Page sub category lists in REC

index.html.twig

{% include "html/helpers/sub-categories-list.html.twig" with {'parent': page.products_shown_cat_id } %}

sub-categories-list.html.twig

{% set subCategories = api('categories', { parent: parent } %}
{% for category in subCategories %}
  <a href="{{ category.link }}">{{ category.name }}</a>
{% endfor %}