Based on this post, you need to add it to your app description:
You need to add this at the bottom of your app description on your store page:
"Terms of Use: https://www.apple.com/legal/internet-services/itunes/dev/stdeula/"
https://www.reddit.com/r/iOSProgramming/comments/1fcr4ih/need_help_with_apple_store_rejection_subscription/
I just had the same rejection, so I added that in my app description and re-submitted. I'll let you know if that's not what I need to do. If so, that's crazy to me. Nowhere in the docs anywhere does it say to do that.
Topic:
App Store Distribution & Marketing
SubTopic:
App Review
Tags: