How to properly add clientCache on IIS 10

I have added clientCache in the web.config file, but Pingdom Tools still tell me to Add Expires headers.

<staticContent>       <clientCache cacheControlMode="UseMaxAge" cacheControlMaxAge="365.00:00:00" setEtag="false" /> 

What am I missing and how can this be fixed on Windows Server 2016 IIS 10?