iTunes byte range request conflict — PHP download server solution?

After submitting a podcast to iTunes, I got this error message: “Your episodes are hosted on a server which doesn’t support byte-range requests. Enable byte-range requests and try your submission again.”

This post and the other pages I’ve found reference https://mobiforge.com/developing/story/content-delivery-mobile-devices as a solution, but I’m unclear on how to implement the provided code. Would it be added to a core file, saved as a separate file, or something else?