Hello BethuneSup ! Flowless app can do it. You can create condition ( or use and correct template): Invoice- Payment reminder, select amount of days before or after due date, then create action: email,sms or voice to company owner, vendor, employee or customer. Hope, it will help you to save tons of time!
I'd be glad to help you today so you'll be able send notices when the invoice the invoice has not been paid yet.
If you're referring to receiving a notice when customer haven't paid the invoice on the due date, as of now, there isn't a way to send you a notice automatically. You have to check the invoices under the Invoices page and check the due invoices manually.
On the other hand, if you want to send a notice to your customer when the invoice is still unpaid on the due date, you can just send another reminder to your customer.
To learn more about reminders, you may check these articles: