Since Zoho Invoice is integrated with Zoho Projects, you wouldn't need to toil over importing your projects into Zoho Invoice to invoice for them. Just when you wish to invoice, follow the below steps to automatically begin invoicing:
1. Click the Invoices tab.
2. On the right-side of the Invoices page, click New Invoice for Zoho Projects.
3. In the New Invoice for Zoho Projects page, select the project name, rate per hour, from date, to date, and the invoice type.
4. When you are done entering all the information, click the Create Invoice button. A new invoice for the project will be created automatically.
Note: Only 'Portal Owners' in Zoho Projects will be able to use this feature.
Zoho Invoice FAQ