Every invoice in the system will fall under one of the following five statuses:
Unsent invoices have been created, but have not been shared with your client yet. You can still receive payment against these invoices. How do I share invoices with clients?
Sent invoices have been shared with the client, but no payments have been made against them. How do I receive payment on an invoice?
An invoice will be marked as paid when all balances due have been paid by the client.
If the balance is not paid in full but a partial payment has been received, it will be marked as partially paid.
When the full total balance due of an invoice has not been received by its due date, the invoice will be marked as Overdue.
An invoice will be marked as forward when any past due balances has been added to the new invoice.
You can filter invoices based on their status. Click the Billing tab, then click Invoices in the gray sub-menu. Then, you'll see blue links for each invoice status (pictured below, next to the first arrow).