To send an invoice or receipt to a client go to Inspections -- Scheduled Inspections. Now locate the desired property and click on Actions -- Invoice (or if you're using the icons view click on the green invoice icon)
This will pop up a screen where you can select an invoice template from the dropdown at the top, email out the invoice, download a PDF of it, or print it out.
If an order has been paid for (or has a total cost amounting to $0.00) it will have a red PAID stamp at the top of the invoice as well.
New Invoice System
Legacy Invoice System