I have the same issue and it seems that the answers are not addressing the questions being asked...

We send an invoice to a customer

The Customer pays the invoice.

Shouldn't my company get an email saying the invoice has been paid? Or at least SOME notification that it's been paid, not that I have to log into my merchant account to check every 5 minutes?

We are getting no notifications that invoices are being paid. Only days later that money is being sent to our bank account. How do I know a customer paid the bill without having to keep logging in?