createFulfillment() - how to get lineItems?

Hi, please help me with this:

I have a backend function triggered by wixStores_onOrderPaid.
I create a package in external system and get the tracking values.
I would like to do createFulfillment() with the values.

createFulfillment has a parameter orderId, so this is fine, however one of the parameter I also need is lineItems.

How do I get the lineItems values based on orderId? I always want to have all the ordered products in the fulfillment.

Thank you