But on the other hand, the key failure point for the app is pretty obvious: its revenue is a one time fee, and the costs are a function of how much people use the app. Based on the post, they clearly mispriced the app, since it depended on new sales to fund existing customers.
This isn't very different from a pyramid scheme (without the intention to fraud, naturally): you need to keep growing indefinitely to stay afloat, clearly impossible. When sales flattened (which they did) the company would go bust (which it did).
Another way to look at this is treating a sale as an annuity. If I sell an app for $10, expecting users to use it for 10 years with a 10% WACC, this would be equivalent to receiving a $0.13 subscription fee from each customer over the 10 years.
Therefore, if your variable cost per customer is higher than $0.13/year, you're in serious trouble. Even if it's lower, you might still not break even.