Apple TV app doesn't recognize my subscription
I just redeemed a free 1 year Apple TV+ subscription from the iPad Air that I bought on December 2019, but every time I open the Apple TV app either from my Macbook Pro or my iPad Air, I still can't watch the series on TV+ because the button "Subscribe to Apple TV+" is present. And clicking it only makes a popup dialog appears with "You are subscribed" text on it.
I have tried re-signing into my Apple ID as suggested by this post, but still no luck.
Any ideas?
iPad Air, iOS 13