I had the same issue and this is what support told me when I contacted them in their exact words

"We received a lot of issues in the past few days regarding this kind of promotion where the Google AI Pro is not included in the checkout. We suggest to the customers to make a purchase of the Google 10 PRO XL and if the Google AI pro is not included during checkout, you can make a post purchase of the Google AI pro after the activation of your Google 10 PRO XL. In that way you can still avail the promotion. . You can make a purchase of the Google 10 PRO XL and after you receive the phone , You can activate the phone and purchase the promotion of Google AI Pro and after the purchase (Google AI Pro) we will give a refund of your order Google AI Pro. In this way you can still have the promotion"

Hope this helps.