Post Paid Billing
Configure your help desk to bill customers per ticket or time based, setup billing rate for each department and create invoice right from ticket. Customers can receive invoice pdf in email and make payment online using credit card or Paypal. This option is good if you wish to bill customers after completion of certain task.
Pre Paid Billing
Create pre paid billing plans with validity period, decide billing cycle (one time or recurring). Allocate credit in terms of points or amount. Customers can order billing packages from client portal and pay upfront. Customers credit will be deducted based on tickets they submit and the billing rate that is defined for services.