iPhone 7 and newer do not have round 3.5mm headphone jacks. In order to connect SleepPhones® Classic headphones to such a device, you will need a 3.5mm to Lightning adapter.
Check the original box your Apple device came in - you may have received a “3.5mm to Lightning” adapter. If not, this adapter will do the trick.
If you have questions, call customer service at 877-838-4790. We want you to have the right equipment to properly enjoy your SleepPhones®.