Extras are additions to the client's monthly subscriptions. They are billed every month in the monthly invoice together with the client's subscription. They can also be discounts, by entering the amount/percentage with the negative sign (-).
Create Additional

Description: Details of the additional charge that will be shown on the customer's invoice.
$ Amount / Percentage %: If a fixed amount is to be used, the additional amount must be charged; it can be negative (-100) to generate a discount. IMPORTANT, the amount is for each month, not the total additional.
If a percentage is to be used, the percentage must be entered, from 1 to 100, and for discount it must be negative. Eg: -100. IMPORTANT: The percentage is applied to the TOTAL of the client's payments.
Months: The number of months that the additional will be active, if you want a fixed additional, set the amount to 99.
Guy: Select the type of additional you want, Fixed Amount $ or Percentage %
% Tax (VAT)): Select the type of tax you need.
Tax Included. If checked, the system will charge that amount as the final amount, otherwise the selected tax will be added. This function is only available in Fixed Amount.
Edit Additional
The additional amount can be edited on any day of the month, the change will be taken into account in the next billing and will not affect what has already been billed.

Remaining Months: The number of months remaining to bill the additional.
IMPORTANT: If you want to modify the number of months remaining to bill an additional amount, you must modify REMAINING MONTHS.