Document Customization


Billing Extension offers you a variety of ways to customize your documents (invoices, proformas, credit notes) from Settings page.

One thing that kind of jumps out at you is the possibility to turn on/off proformas and credit notes individually. WHCS does not natively support credit notes and can't even accurately distinguish between invoices and proformas. Thanks to our module it is now possible to categorize all these three types of document with absolute certainty. Let's first analyze the settings that all types of document have in common.

Common Settings

This part of documentation applies to every document type (invoices, proformas and credit notes). Each of them has its own Number Format, Next ID and Increment.

Number Format represents the format you want to use for the numbering of your documents. It doesn't just have to be a number. You could for example include a special prefix or suffix (eg. KATAMAZE-{NUMBER}). {NUMBER} acts as a placeholder that gets replaced with the number of your document (eg. invoice number). WHMCS offers 4 placeholders but in Billing Extension there are new ones more. Here is the complete list:
If you use an Electronic Document Management System (EDMS) you can categorize and archive all your documents as you like. Your format in fact is used also as file name for PDF files. Let's see how you can use the available placeholders to create your own style:
  • {COUNTRY}-{NUMBER} becomes US-125
  • {MONTH}/{USERID}-{NUMBER} becomes 12-2-125
With Next ID you can change the next number to assign to your document. This number affects {NUMBER} placeholder and allows you to regenerate missing invoices or to start from a specific number instead of 1 which is useful in case you are migrating to WHMCS from another system. Please be very cautious if you change this value since you could cause documents having duplicate numbers.

Every time a new document is issued the next number to assign is increased by 1. In most of the cases invoice numbering needs to be sequential since it's required by the law in multiple countries. That's why generally you shouldn't change ID Incrementation for invoices so that you have no no gaps in your sequence (1, 2, 3, 4...). That said no one forces you to use the same approach for proformas. Here you can deliberately decide to leave empty "holes" in the numbering sequence. Say that you set this value to 5. Proformas will follow this sequence 1, 6, 11, 16...


Invoice Date on Payment must be enabled if you are an European company but this rule is valid also in other countries. When this option is enabled, the module not only makes sure that invoice numbering is sequential but also that invoice dates are sequential. As soon as an invoice is issued, its date corresponds current date. In this way you don't have to worry about invoices going back and forth through time. This setting also applies to credit notes if in use.


If you want to get rid of proformas, you can disable Proforma Invoicing so that WHMCS generates just real invoices. For a variety of reasons described here we reccomend you not to do so.

Credit Notes

Similarly to proformas, credit notes can be disabled by turing off Credit Notes. Read this article if you need help choosing if this option is good for you. Since the only difference between invoices and credit notes is that the latter have a negative amount, they can both use and share the same numering (eg. Invoice #1, Credit Note #2, Invoice #3). If you want to keep them separated, enable Dedicated Sequential Numbering.

When the option we just mentioned is in use, it brings up the usual settings (Number Format, Next ID, ID Incrementation) and a special one named Identifier. We suggest you to use the Identifier to avoid any possible confusion between the numbering of invoices and credit notes. Let's assume that we're using the same configuration for credit notes and invoices. We could end up with this scenario:
  • Invoices: 2018-1, 2018-2
  • Credit Notes: 2018-1
Even though we're using a dedicated sequential numbering for credit notes, some of them may look like duplicated invoices. This is the case of invoice 2018-1 and credit note 2018-1 of the example describved above. Even if they effectively are two distinct documents, they look like duplicates. That's where the identifier comes to help. It can be just a letter (eg. B) used to mark credit notes. This way the credit note of the previous example becomes 2018-1B.