The new billing system is continuously being improved to provide the best experience possible but we are aware that there are still issues that need to be resolved. One aspect that has been improved today is that invoice reminders have been improved to avoid excessive payment reminder notices and alike from being sent to clients. Going forward, you should see dramatically fewer reminder notices in your inbox.
We apologise for the poor experience some clients have had with this, particularly when payment is made on time but done so via bank transfer.
For curious persons, the reason for invoices not being marked as paid quickly is that when the payment method is a bank transfer there are delays introduced by the transfer time at the bank level, and then the bank feed sync interval at the accounting software/service level. This can introduce a delay of 5-6 days before we are able to automatically mark the invoice as paid.