Verify that you are eligible. If you have enjoyed an extended free trial before, then you can’t have another one. Redeem within the first 90 days on your new qualifying Apple device, in the TV app. Find the “Enjoy 3 Months Free” redeem button there.
Read here how to redeem: Apple TV+ offer - Apple
Read here about the conditions: Apple TV+ offer - Terms and conditions - Apple
Read here if you have trouble redeeming: If you can't redeem your promotion for an Apple subscription - Apple Support
↳ Step 5 says to contact Apple if the prior steps didn’t bring a solution. They can assist.
iPhone 8, iOS 14
iPhone 8 has been discontinued since 2020, and wouldn’t qualify today.
I’ve bought several iPhones
Just one will do. More doesn’t change anything. You can’t claim more than once.
The offer covers the last 90 days. What you bought before Dec. 7 doesn’t count.
The offer is for the first registered user of that new iPhone. What you bought for others doesn’t count.
The offer is for devices from Apple or from Apple Authorized Resellers. The unlicensed corner shop doesn’t count.