If you do not want to invoice all your Ready to Invoice tasks in a payment period, you can remove some of them from an invoice. These tasks will then be available the next time you submit an invoice.
Select Invoices > Ready for invoicing from the main menu
Select the Raise Invoice button from a Ready to invoice task card
Port will create an invoice by default which includes all your eligible tasks.
From the task list, select the Remove task icon for the tasks you would like to remove
This will remove the selected tasks from the current invoice.