Free trials are great for conversions, but Apple has strict rules about how you disclose what happens when the trial ends. If users can't easily find the price, duration, and cancellation process, you'll get rejected.
What Apple said
“Your app offers a free trial but does not clearly indicate the duration of the trial period, the price of the subscription after the trial ends, or how users can cancel before being charged. This information must be clearly disclosed to users before they subscribe.”
Apple requires that users know exactly what they're signing up for before any money changes hands. That means the trial duration, the post-trial price, the billing frequency, and how to cancel all need to be visible and legible before the user taps 'Start Free Trial.' Burying this in fine print or a privacy policy doesn't cut it.
While you're at it — Apple also requires these pages for every app.
Fix this rejection, then make sure you're covered on the compliance side too. Apple requires every app to link to a hosted Privacy Policy, Terms of Service, Support page, and Data Deletion page. No link means another rejection — just for a different reason.