Additional info, there’s no way to create Project Transaction from here?

I don't this is possible. 

Create Project Transaction would be a good idea to have at least as an option.

Hi,

If you have rented to a customer, you should have created a customer order and connected to the project and rented out parts through the customer order. 

Then you can create the regular customer invoice which will report revenue to the project. 

The purpose of rental functionality in the Misc Rental Info tab is to rent out parts for the use of the Project and not to external customers. 

Hope this helps?

AsankaD