(expiration not specified) - Poor Leverage Browser Caching

Hi
My speed test keep saying that I have poor "Leverage Browser Caching" because the (expiration not specified) for certain files.
I have the expiration date set to one week in my settings.
What am I missing?
Thanks
My speed test keep saying that I have poor "Leverage Browser Caching" because the (expiration not specified) for certain files.
I have the expiration date set to one week in my settings.
What am I missing?
Thanks