Thanks for keeping in touch with us here in the Community, @Catherine1955.
I appreciate you for doing the steps suggested by my colleague @katherinejoyceO.
Since you're still having this issue, you can attempt deleting the invoice and recreate it.
Here's how to delete an invoice:
- Go to the Customers menu.
- Select Customer Center.
- Choose the invoice created with 30 days term.
- Open the invoice then click the Delete (X) icon on the upper part of the invoice.
- Click OK.
Then apply the 30 days term again.
When you're ready to enter payments for your invoice, you can check this article for your guide: Record an Invoice Payment.
Get back here in the Community if you've got additional questions. I'm here to help you. Have a good day and you take care!