Yes, when you purchase an upgrade for Zenkit To Do, you will be asked how many "seats" you want to upgrade. This is the number of people who can collaborate in your account. This refers to the people who are members or lists within folders that you own, or members of folders that you own. You can learn more about this on our pricing page.
Lists that are inside folders owned by other people will not be covered by your subscription.
If you would like to pay for a subscription for someone else's account, please contact our sales team at firstname.lastname@example.org.