Virtually all customers who purchase month-to-month servers will find a one-time fee added to their first calendar month bill as a new customer, or when new services are added.
All services are billed by the calendar month, so the billing period for your services will always start at the first of the month. If you order a new service or are a new customer, the start date will often not be the first of the month. This is why there will be a one-time fee added to your first invoice showing the new service or, as a new customer. This covers the phase between the start of your service (i.e. the day on which the server is ready to use), and the first day of the next month.
This one-time fee will also appear on the official invoice for your administration.