Users have 90 days to redeem the offer for the extended trial. After that time, only the regular 7 day trial will be available to new subscribers.
Current and previous subscribers have already tried Apple TV+, and may not be eligible for a new free trial.
If you are eligible, then redeem on your new qualifying Apple device, not on a different device.
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.