small but important billing improvements

[Remitur]

Billing and invoicing features may change in different country; what is lawful in a country, may be unlawful in another one... there're few possible billing improvements, which should be easy to set up (for WHMCS), and may be used to accomplish local requirements. I'll try here to point them as optional settings, which every user may be able to set up as needed:

• don't allow partial payment with credit
  I.e.: a user has a proforma of 100, he has 30 of available credit => he pays only 70 (by credit card, paypal etc) and 30 by credit
  This may be both an accounting and fiscal issue.
  Fix: 
  - in "general setting" => "billing" insert a check "don't allow partial payment with credit"
  - if set, the customer has the option to apply credit to a proforma only if his available credit is greater than the amount of the proforma
   
• never allow partial authomatic payment with credit
  i.e.: a domain has auto-renew enabled; the available credit is not sufficient; WHMCS issue a proforma, does a partial payment using the available credit, and leave the user to pay the missing amount elseway...
  This is ALWAYS an issue, because if the user doesn't pay the missing amount, the domain will not be renewed, but a partial sum has yet been paid, and cash back this sum to the user has to be done manually...
  Fix:
  - authomatic payment of proforma using credit is done only of available credit is greater than the amount of the proforma
   
• option: don't convert proforma paid in full with credit in "paid" invoices
  i.e.: a customer has 1000 domains; he did only 12 monthly "credit charges" yearly, to pay all of his domains by autorenew
  just now, WHMCS will issue around 365 proformas, will pay each of them individually, and will convert all of them into "paid invoices", of zero value.
  So both the reseller, both the user will need to account 365+12=377 invoice yearsy (instead of 12), most of them of zero value.
  In many countryes the issue of an ivoice is mandatory only if there's a payment, and for payment with credit (which has been previously invoiced) it's not mandatory to issue a "paid" invoice.
  So, there're 365 unuseful invoices of zero value...
  Fix: in  "general setting" => "billing" insert a check "don't convert proforma paid in full with credit in "paid" invoices"
  if checked, the proformas paid with credit will remain proformas, with their own original numeber, and with a reference of the payment using available credit
    

Edited December 28, 2017 by Remitur