Posted by: netshine
No, I don't think it is a problem with nBill at all. nBill is only adding a single income record - something outside of the nBill core is adding an additional record. It could be your payment gateway script. I see you have the auth.net gateway, but has it been modified or extended at all? Do you have a silent postback URL defined in your auth.net merchant interface? (if so, try removing it) Do you have any custom scripts or custom code running? Do you ever mark invoices as paid yourself?
Yes I mark invoices paid myself when I use authnet, because it doesn't do it automatically, and sometimes when i use paypal because of the same above reason. So why would it create 2 receipt numbers?