In amoCRM there is a limit applied on the number of users in a single account. The number of licenses is limited by the subscription plan and you previous payments.
In case you need more users for your account, you can buy additional licenses without extension of the subscription and changing of the plan.
To buy more licenses for your account, go to section Settings -> Billing and choose your current plan:
In section “Buy licenses” enter the number of user you’d like to buy in addition to the existing ones:
Switch off Subscription and press CHECKOUT to proceed with the payment
Important: if you’re buying additional licenses, total amount will be calculated using current expiration date of your account.