as you have in ZOHO project, You are able to make subtasks.
With invoices this is not possible.
So you could invoices the subtasks but you can log you hours for later references and new projects.
For example.
This is for project A for Client 1
Prestudy is something i would like to invoice to my client.
In the pre-study phase, I have to do some tasks like getting base info, talking with stakeholders, setting up meetings, making meeting reports.
All the tasks I don't won't to place on the invoices, just pre-study the rest of the info is for internal use. for the next project.
For project B for client 1
We are in the basic engineering phase, this is the only thing i wont the see on the invoice is for project B for basic engineering 20h at 50€/h.
All the task I have to to for example making business case, preparing budget proposal, meeting with team, meeting with stakeholders, ect.
I don't want to see on the invoice.