if i have already free subscription of tv and im gonna buy new product with another free subscription for one year can i use it one after another?

From this document:Get one year free Apple TV+ when you buy a new iPhone, iPad, iPod touch, Apple TV, or Mac https://www.apple.com/promo/pdf/EN_US_ATV+_Promo_TandCs.pdf

"Offer cannot be combined with other free trials or offers for Apple TV+. "

No. There's only one free year of Apple TV+ per Apple ID or Family Sharing group.

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