When an invoice is created it is assigned a numerical identifier known as the Invoice Number:

The format of this invoice number can be customised with text and different numerical sequences in several ways to meet your accounting requirements, for example:

• ABC-123
• 01-01-2020~456
• IND/789
• ANYTEXT-2020-123

Follow these steps to configure WHMCS with a custom invoice numbering sequence:

1. Navigate to Configuration > System Settings > Tax Configuration (prior to WHMCS 8.0, Setup > Payments > Tax Configuration).

2. Toggle the Tax Support option to the On position

3. Toggle the Custom Invoice Numbering option to the On position

4. Use the Custom Invoice Numbering Format field to specify the invoice numbering format you wish to use.

The field can contain characters to be contained in the invoice number that the client will see. Additional tags can be added to the field which will be replaced as the invoice is generated. Available tags are:

• {NUMBER} - This is the value of the Next Invoice Number field
• {YEAR} - The four digit year value for the current date
• {MONTH} - The two digit month value for the current date
• {DAY} - The two digit day value for the current date

For example:

• ABC-{NUMBER}
• {DAY}-{MONTH}-{YEAR}~{NUMBER}
• IND/{NUMBER}
• ANYTEXT-{YEAR}-{NUMBER}

5. Use Next Invoice Number field to specify the number to be assigned to the next generated invoice.

6. Click Save

The next invoice to be generated by WHMCS will be assigned an invoice number according to the custom format and number sequence specified.

In this example the next invoice will be assigned the invoice number ANYTEXT-2020-123