An invoice can have one of seven statuses.
The invoice has not been sent to the client yet. Payments cannot be applied to a Draft invoice.
The invoice was emailed to your client but has not been viewed in Canopy.
Your client has viewed the invoice in Canopy, but has not made any kind of payment yet.
Your client has made a payment, but there is still an outstanding balance on the invoice.
Your client has made a payment, but the invoice is now overdue, and still has an outstanding balance.
No payment has been received and the invoice is also overdue. Bad news...
Good news! You got paid!