Did you check the eligibility on this Apple page?
Do any of these points apply to you?
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- $6.99/month after free trial. Only one offer per Apple ID and only one offer per family if you’re part of a Family Sharing group, regardless of the number of devices you or your family purchases. This offer is not available if you or your Family have previously accepted an Apple TV+ one year free offer. Offer good for 3 months after eligible device activation. Plan automatically renews until cancelled. Restrictions and other terms apply.
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copied from: Apple TV+ - Apple
