How is profit reported if I didn't enter costs?

Cost is an optional field. Products without a cost are left out of profit, while their revenue still counts in full. The Profit Tracked card on Stats shows how many products sold in the period have no cost; a cost of 0 counts as a cost, so those products aren't listed.

Tap the card or View products to open Products Without Cost, ranked by the revenue left out of profit. Tap a row to open the product, add its cost from Edit, and the row is marked Cost added when you come back. A product with variants is marked Cost added only once every variant sold without a cost has one — its own, or the product's cost to follow.

Profit is revenue after every discount (item and cart discounts, promotions, points redemption) and before tax, minus cost — which is why the field reads Cost excl. tax (optional): enter what you paid before tax. Margin is profit ÷ the pre-tax revenue of products with a cost, so products without one don't drag it down. A return takes back, on the day of the return, the profit those items had brought in.