Offtoa uses many of your stated assumptions to compute the COGS, so any of these could cause COGS on your income statement to be zero:

1. Raw Materials. You might have no raw materials. On the menu, select assumptions/costs/raw materials. This might be perfectly valid if you are a software company or a service company, for example. This is not acceptable if you are in manufacturing, wholesale, or retail industries.
2. Price of Raw Materials. The prices you pay for all your raw materials could be zero. On the menu, select assumptions/costs/raw materials.
3. No Raw Materials Used in Your Products. You may have indicated that no raw materials are being used in your products. On the menu, select assumptions/costs/cost of goods sold.
4. Not selling any products. If you don't sell any products during this period, you will not have any COGS.

Related Questions:

How does Offtoa calculate cost of goods sold?

Where do I enter/change raw materials?

How do I relate raw materials to products I sell?

Why do I have zero COGS for just one product?

Why do I have zero COGS for just one market?

How do I change the price of a raw material?

How do I change the number of units that I expect to sell?

How do I suppress a line of all zeros from a report?