One of the most important questions in using unit economics is what to count as COGS and what not to count. On the one hand the entrepreneur, wants to account for all costs in the business to understand how many customers are needed to recoup all costs. But that's not the right way to do it! COGS isn't a catch-all.

The first thing to remember is that the task of unit economics is to calculate the effective marginal profit of the business, which will already cover the costs. At the same time, the marginal profit is connected exclusively with direct commercial activity - with sales. Therefore, COGS includes only such variable costs, without which this activity is impossible to carry out. 

The second rule, try not to include all fixed costs in COGS, such as wages and rent. 

Third, there are situations where a business needs to buy servers based on the number of customers, and it seems that server costs are COGS, but often they are not. If your server fees don't decrease as your number of customers decreases by even one unit, then it's not COGS.

The best example of what is COGS is acquiring.

And remember, in your business model, COGS can be zero.