Why can't I buy Apple Care for my new iPad?

I received an iPad Pro as a gift in February 2021. It just died and was replaced under the one year limited warranty….I did not purchase apple care for it, I want to purchase apple care for the new one , but it says it is not eligible when I type in the serial number. How do I get apple care for the new one? Today is Wednesday I been trying since Monday late afternoon but to no avail, the tech told me I had only 7 days (now I am not certain if day 7is Sunday or monday)

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