A review of the cash sales invoices determined that one sale of $450 (cost of merchandise $142) was unearned.
This is saying that it has been recorded but have to undo the sale and you have the cash.

Is this correct?
Dr. Unearned sales
Cr. Sales
Dr. Inventory
Cr. Cost of Goods Sold

Dr. Sales 450 (take 450 out of revenue)
Cr. Unearned Sales 450 (add 450 to unearned)

Dr. Inventory 142
Cr. COGS 142