Introducing Invoicing app extension!
If you want to develop or are developing an app with an invoicing capability this is for you.
Now, apps with invoicing capability can extend their functionality to the Invoice tab in Pipedrive’s Deal details view. This will enable app users to create and edit invoices directly from Pipedrive.
Read more about it in the documentation: https://pipedrive.readme.io/docs/app-extensions-invoicing