my one care subscription has expired. I get 1 year for up to 3 pcsi have only used one year on my pc and was wanting to add the other two years but my product key says not valid
You can’t trade the unused installations for extra years, since this is a standard 1-year license. You’ll have to purchase a new subscription online, or buy the retail package and use the product key as payment: https://billing.microsoft.com/home.aspx
You can usually save some money by shopping around for a bargain on the retail package. Since you’ll then be using the product key to “purchase” the subscription, the subscription service will refer to the product key as a “token”.