Overdue Customers - Just need warning

Thanks for joining the Community, @DiogoIannaccone.

I can see how it would be useful to have the big warning pop up before invoicing any customers with overdue. That said, I'd suggest sending feedback straight to our product developers/engineers to be considered in the future. They are constantly finding ways to improve our product and service to make QuickBooks work the way your business needs. 

1. Go to the Help menu and select Send Feedback Online.
2. Click the Product Suggestion from the dropdown menu.
3. Fill out the on-screen instructions in the QuickBooks Feedback window.
4. After that, click Send Feedback.

I also encourage you to visit our Firm of the Future site to be updated with our latest news including product enhancements: Firm of the Future.

In case you need to invoice customers with overdue, you can uncheck the Do not sell to overdue customers box. Then check the box again, if you need to use the feature again.

Once everything is settled, you can now print and email your invoices. Moreover, I have here an article that you can use for guidance in case you need to personalize how your invoice looks and make your company stand out: Use and customize form templates.

Please let me know if you need further assistance with your QuickBooks account. I'm here to help you out whenever you needed me. Have a great day, @DiogoIannaccone.