How can I associate certain expenses to item fulfillments? For example if I pay a shipping company for a certain SO how can I somehow attach that expense to the item fulfillment? Sort of like Landed Costs for item receipts though I need it for item fulfillments.

Do you mean to bill the customer ? Gl impact ?

We want to do a P & L by customer but we need to include other bills that were billed to a separate vendor.

Does the customer pay for shipping cost

No we do.

The IF will (am half sleep so I can't rember my credits and debits) hit inventory asset and cost of goods sold ,the invoice if I'm not mistaken is accounts payable and sales ,which account does shipping cost hit?

COGS usually but can be a different account sometimes.

From booking perspective landing cost is just added cost to the value of an asset . How can shipping cost be attached to a sale that isn't billed what two accounts do you want it to hit

I want it two hit different accounts but I want a way of associating it with a given customer to be able to run reports.