If you use other software to bill your services, you can activate external billing. You can find this setting in the system settings for customer invoices.
External billing #
External invoicing provides you with a simplified dialog for creating invoices.

Data export #
You have the option of selecting predefined export data structures in the Data export area. The available options are customized and continuously expanded.
Once you have made your selection, click on the clipboard icon to paste it into your billing software.
Post invoice #
Enter your own invoice number in the “Invoice number” field. The number must be numerical and unique. If this is alphanumeric, you can also enter this in the field after the invoice number. The invoice number remains empty in this case and is assigned automatically by the system.
In the Amount field, enter the amount, the currency and the desired VAT. It is possible to use only one VAT rate in external data entry.
Complete the booking by clicking on “Save”.