To buy new Imunify360 license(s) go to Billing → Purchase. Here you can see the number of your Server Licenses (used/limits).
Specify the number of server licenses for each License Type (Single User, Up to 30 users, Up to 250 users, Unlimited) and choose Payment method (monthly or early). Your current price is displayed on the right side. The prices depend on the number of server licenses that you already have (or will have after the purchase). The bigger the number of server licenses, the lower the price.
Then click Add to Cart. This will activate Cart menu in the top right corner of the page. To complete your purchase, click Cart icon, you will be redirected to the Cart page. To remove a purchase from the cart, click Remove From Cart button.