When it comes to accounting for drop-ship purchase orders, there are a few differences from regular purchases orders.
Invoicing drop-ship purchase orders
Drop-ship purchase orders should have a purchase invoice received against them in the same way that regular purchase orders do. The key difference between drop-ship POs and regular POs is that you don't receive any items into stock from a drop-ship PO, so there is no impact to your inventory asset value.
Nominal codes
Items on drop-ship purchase orders, even if they are stock tracked items, are assigned a purchases nominal code (5xxx) since no items are received into stock. Normally a purchase order for inventory would have an asset nominal code (1xxx).
The purchases code on the PO line will be the one defined on the product, unless the supplier has a nominal code set.
When a purchase invoice is received against a drop-ship purchase order, the net value of the items is added directly to the relevant purchases nominal code, accounting for the cost of goods sold.
Invoicing drop-ship sales orders
You will need to invoice drop-shipped sales orders to complete all accounting processes. A sales invoice (SI) journal will be added into accounts, recording the revenue and tax side of the sale.
However, since you didn't carry the stock, there will be no cost of goods sold journal which is normally associated with a shipped goods out note. Instead, cost of goods sold are accounted for when the purchase invoice is received.
Cost tab on sales orders
The costs tab on a sales order shows prices from the cost price list selected for that order, unless items have been allocated or fulfilled from a warehouse - in which case the actual FIFO value of inventory is used.
If you create a drop-ship PO for a sale, the PO price will only show as the cost value for the sale after the PO is invoiced.
Costs vs revenue dates
Revenues will be posted to accounts at the tax date of the sales invoice, and the costs will be posted at the tax date of the purchase invoice. Be aware of this when you are reporting on profitability of your drop-shipped sales.