Hello

Can you share your data model, ER diagram that can help us understand how you are doing this

Thanks

So what you can do here , when you are ready to create an order for the items in a cart,

Create the order with all the details which are required on your order table, Once the order is created now you have an Order Id which your Create Order action will return. Now For each of the products (order Items) pass the same Identifier order Id that is created to the reference attribute of an order detail Extended entity so it will loop with all the product that is in your cart that have a product Id but the Order Id remain same for each record that get created.

hope this helps