This is the same for most eCommerce stores. The integration by default uses the product Type name in Retail Express.
We can support multiple subcategories in WooCommerce and BigCommerce by separating each category in Retail Express with '-'. There is no need for a space between these and try to avoid strange characters like Ampersand & and of course do not use a dash for any other reason like T-Shirts. Also, try to avoid confusing duplications like Mens-Shirts and Womens-Shirts. As it updates products it will add the subsections, You should not add any category yourself to avoid confusion.
We will attach the product to ALL of the categories including the parent. Retail Express does not support more than one category beyond this.
So MENS-T-SHIRTS will go in to
MENS
T
SHIRTS
We attached the product to every category then including the parent.
Retail Express does not support more than one product type per product. So with some systems like WooCommerce and BigCommerce you will be limited to the product being in one category, or not updating the Category after it is sent.
For example:
