What is the data processing fee in Azure DDoS Protection Standard, and when is it applied?

The data processing fee is charged for traffic that is inspected and potentially mitigated by Azure DDoS Protection Standard during an active attack. This fee is calculated based on the volume of mitigated traffic (in GB) and is only applied when the service detects and actively defends against a volumetric or protocol attack. It is designed to be a pay-as-you-go charge for the mitigation effort.