[Plugin: WP-Invoice – Web Invoice and Billing] No email notification on payment though option is set

Version 3.04.4
Two of my clients paid me with PayPal using this plugin. I received no email notification from the plugin, even though I have that option set.

I know the email sending works because I tested the plugin Send Notification function, plus those clients got the email and paid.
My email works because I received other email on it.

https://www.ads-software.com/extend/plugins/wp-invoice/