According to the terms by Apple,
"This offer is not available if you or your Family have previously accepted an Apple TV+ one year free offer."
What is really annoying about the whole process is that Apple knows all about my Apple product and subscription purchases and yet does not use this data to provide me with a viable free offer. Nor can support even come close to telling my how to use it.
If it is even possible, I would have to cancel my current yearly Apple Plus Subscription one day before it is due to renew, then try to apply the 3 month bonus offer, then cancel it again after the first month of paying $5/per month so I could resume the yearly rate of $50.
How is this a benefit to one of Apple's best customers? It is not. Why offer a benefit after purchase that cannot be applied easily.