That is due to the payment terms that you set on the invoice, @bustillo.
First, you’ll need to add a payment term that is due within 30 days from the invoice date. Here's how to do it:
1. Go to your Lists menu and click on Customer & Vendor Profile Lists and then Terms List.
2. Click the Terms drop-down and choose New.
3. Provide a name for this term and then choose Standard.
4. Select OK.
Check the following article for more information about this: Set up payment terms.
You can now create an invoice that'll show past due in 30 days. To know more about how to add the Past Due stamp from the templates list and directly from the invoice, read the following article for detailed instructions: Show Past Due stamp on invoices.
Let me know if you need further help with those payment terms. The Community is always glad to help in any way we can. Have a wonderful day!