Use the Add field button to add one or more fields to the format. The counter field is mandatory, otherwise the invoices are not numbered automatically.

Here are a few predefined formats:

1. counter (001) Use it
2. year-counter (07-001) Use it
3. client code-counter (CODE-01) Use it
4. prefix date-counter (P 012807-0001) Use it

The format requires a special syntax that is (hopefully) simple. Each field is surrounded by ${}. The suffix ?string("") indicates how a field looks.

For instance, if the counter field is used as ${counter?string("000")} it means that it is represented as a three digit value. If the date field is used as ${date?string("yyyy")} it means that only the year will be displayed.