An Additional Tag stops with "this tag adds another vehicle to an account that already has an active KOVA subscription, and this one does not have any" when the account being signed in to has no live subscription.
A Replacement Tag stops with "no active vehicles found on this account" when the account has no vehicle to replace a tag on.
Both are usually the same underlying cause: the customer signed in with a different phone number from the one their vehicle is on. Check which account they are in before anything else.