In billing, I set Service Invoice Threshold to 15 days and Invoice Grace Period to 15 days. That should mean an invoice is raised 15 days before the due date DUE in 15 days and suspended 15 days after the due date. However, what is showing on the invoice is DUE in 30 days (15+15) which is not correct.
I also don't think there are enough reminder notifications. It would be good for the admin to be able to decide when to send reminders. For example, to be able to send a reminder 7 days before the due date, on the due date, 7 days after, then at 15 days when suspended, etc.