Currently, when sending an invoice with a payment schedule, both the default system-generated email template and the custom email template (assigned in Global Invoice Settings) are firing at the same time. This results in the customer receiving two invoice emails for the same scheduled payment.
This behavior creates confusion and inconsistency — especially when only one of those templates has been intentionally customized to reflect the brand voice, payment terms, or special instructions.
For regular one-time or recurring invoices, the system correctly sends only the selected custom email template. But for payment schedule invoices, it appears the system does not respect the global template setting, and the default email is sent alongside the custom one with no option to disable it.