Agree. Such behavior is unacceptable for a paid service. I can understand there would be bugs etc., but leaving draft invoice dangling there without any alarms

Agree. Such behavior is unacceptable for a paid service. I can understand there would be bugs etc., but leaving draft invoice dangling there without any alarms raised is beyond reasonable. Let invoices go out and help the client collect the money on time is vital for such products. It's eye-opening to see someone blaming the business owner instead of the software vendor.