After creating orders sheet child. i have created child line items from order worksheet.
I have adding product name and price field and then selecting derived field in type dropdown after then I am adding new field as product name and price then selecting lookup field derived type. Please check attached video file.
i am not sure if I understood the issue well…but seems like you are trying to access field of catalog in line items whereas you have not attached catalog as linked dropdown to line item worksheet…if you do that, you can access fields of catalog in line item…
so basically you need to have orders and line items as parent child, and in line item you should add catalog as link dropdown to create your order table layout…hope it helps…
Best,
SB