Hi @Mary Nic,

Thank you for joining the thread, as well as sharing the details of the steps you've taken so far. 

Since you already went through the troubleshooting steps provided by my peers above, it's best to speak with our Technical Support team for further assistance. They can pull up your account information within a secure environment, and investigate why you have this issue. 

See this article for the steps: Contact QuickBooks Desktop support. Please take note of our Technical Support team's operating hours, so you know when they're available. 

If you want to apply discounts to early payments towards an invoice, see this article: Record an invoice payment. Scroll down and look for the To apply a discount for early payment section.

Post a reply if you need further help with net terms on your invoices in QuickBooks Desktop. I'll be around to help you out.