How to include multiple projects on one invoice?

I have a $20 subscription to Zoho PROJECTS.

I have a free subscription to Zoho INVOICES.

From within PROJECTS I have activated the Zoho INVOICES integration so that I can easily create invoices for the work I do in PROJECTS without having to leave PROJECTS and launch INVOICES.

THE PROBLEM

The only way I can create an invoice in PROJECTS is to first click on a Project then the side menu appears and I can create an invoice but the invoice will only feature work from that Project - not any other Projects inside PROJECTS.

I would like to be able to create an invoice that includes work done on multiple Projects. I have 2 main clients. Each one has multiple Projects that I work on. I would like to be able to send each client a single invoice that lists all the work I've done for that week.

I do not want to create a separate invoice for each Project - if I did that I may end up having to send each client 10 or more invoices, some that may only involve 5-minutes of work.

THE QUESTION

How do I create invoices that include multiple Projects?

Dan.