Before starting any usage or setting of the Invoices plugin, you have to active the module for the particular project that you are going to use. So, please go to Project settings - Project tab - Modules (at the bottom). Here, enable the Invoices plugin module and save the changes. You may check the following screenshot reference to make the situation more clear:
Note: Please keep in mind that the Contacts module (plugin) is also needed for the Invoices to be able to work. It is stated in point one of the Invoices installation guide.
Once you have enabled the module, then additional Invoices plugin project setting tabs will appear:- Invoices
- Invoices template
