Thank you again @sunnyson !
There is something wrong. My client needs to be able, from the administrative panel, to check the orders her clients have paid so she can send them their product(s). Right now she has only the ids of OrderDetails in Orders in the admin panel. Should I use a component for this ?
Also when I think about it, I don’t need OrderDetails to be a Content-Type since I won’t do any request on it.
I just need a nested “details” (products and quantity for each one inside) in “orders”.
This is very basic normally, I don’t get why it’s that hard 
Btw is it normal controller isn’t call (to check the body of Strapi’s requests for example) ? It only goes through my create(ctx) function while I use API requests, not directly Strapi. I would like to be able to have control on both (Strapi’s administrative panel and API requests). If it’s not the case, I guess I’ll have to duplicate the code ?