Each Manager or Statistician Account allows for the first block of 50 locations.   Use this should you need to have more locations within an existing account.  If you want a new user account  then add a dashboard account instead.

You can buy additional licences in blocks of 10 or 50.   Use quantity to select what you need e.g. if you need up to 80 locations in your licence:  select 3 x 10 to add 30 locations to your original licence of 50.