Hello there, @bae1bae1.

I'll help you fix the terms of your invoices in QuickBooks Desktop. Net 30 should show 30 days after the invoice date.

I suggest checking the Net 30 terms and ensure it is set correctly as the automation of the due date depends on the payment terms setup.

Here's how:

1. Choose the Lists tab from the top menu bar.
2. Select Customer & Vendor Profile Lists.
3. Click Terms.
4. Open the Net 30 term.
5. The box for the Net due should show 30.
   

You can then create a new invoice to check if it will now show the correct date.

If the issue persists, you can update your QuickBooks Desktop to the latest release to ensure you'll have the best experience with QuickBooks. Refer to this article for the detailed steps: Update QuickBooks Desktop to the latest release.

Once done, you can run the Verify Data and Verify Rebuild tools. It will help identify the issues within a company file and resolve them using Rebuild Data.

To run Verify Data:

1. Click the File tab at the top menu bar.
2. Hover your cursor to Utilities.
3. Select Verify Data.

Next, run the Rebuild Data option through these steps:

1. Click the File tab at the top menu bar.
2. Hover your cursor to Utilities.
3. Select Verify Rebuild.

Additionally, I've attached an article you can visit to know more about how to enter invoice payments in QuickBooks Desktop: Record an invoice payment.

Feel free to click the Reply button below if you have questions about managing invoices in QuickBooks Desktop. I'm always here to help. Have a great day.