clockodo focusses on tracking your worktime precisely and analyzing that data by your needs. For invoicing purposes, there are many excellent applications. We integrate them into clockodo to easily transfer your time entries into invoices. We have extended this service to support more billing software. Please have a look at this tools to find the one which fits to your needs.
To get an overview of the invoicing workflow, please have a look at this blog post. If you use another invoicing tool which offers an API, don't hesitate to contact us. We will check and probably integrate it if possible.