Invoice Time Spent on Tickets (Postpaid Support Services)
Directly pull the billable time you have tracked on your helpdesk tickets into sales orders and invoices through a project task. It gives you more control over what you charge your client, and it is more efficient.
Go to Helpdesk ‣ Configuration ‣ Helpdesk team ‣ Edit and enable the options Timesheet on Ticket and Time Reinvoicing.
Under Timesheet on Ticket, choose the Project to which tickets (and timesheets) will be linked by default. Open its External link to enable the feature Bill from tasks.
Create a sales order
Now, once you have recorded the time you spent on the helpdesk ticket, under the Timesheets tab, access the task clicking on its name.
Create Sales Order and proceed to create the invoice.