Why I can’t purchase AppleCare+ for my IpadPro?

Hi,

I purchased my Ipad Pro 11” yesterday from local carrier Vodafone, i tried to go into General-About, couldn’t find any AppleCare +. So i tried to search online and type in my serial number, it show that my ipad is not eligible to buy! But my another Ipad Pro which is bought 1 months ago still can buy?