For a service that is billed based on a metric that only be measured by the provider, that provider has an important responsibility to accurately measure the me

For a service that is billed based on a metric that only be measured by the provider, that provider has an important responsibility to accurately measure the metric, because important financial and technical decisions will be made based on that information. The fact that the metric was under-estimated (and therefore the costs were lower than they should have been) certainly constitutes some kind of compensation, the actual damages might be far beyond the temporary reduction in costs. A feature might be rolled out "as is" to the entire user base after it was determined, on a small sample, that the costs per user were acceptable ; if the costs were greatly under-estimated, the company is left with a choice of discontinuing the feature (angering users) or scrambling to optimize the software, possibly starting from scratch with another technology. Or a yearly budget might have been designed based on usage estimates, only to be revealed as insufficient once actual estimates become available, and requiring an emergency cash injection for the company to pay for it. I'm not a user of Firebase, but if our cloud provider (Microsoft Azure) were to announce that our costs had been underestimated by 2x or more, we would sue and argue that a 50% cost reduction for the past few years does not even begin to cover the strategic impact of the incorrect metric.