Thank you for reaching this to the Community, @InfoDevPro.

Currently, there’s an open investigation about clients who are unable to pay an invoice sent through QuickBooks. Our engineers are working on this to fix the problem as soon as possible.

At this moment, you can perform some troubleshooting like using a private browser. It ignores websites from using cookies and doesn’t record any history and data.

Here’s how to do the private browsing:

• Safari: Control + Option + P
• Google Chrome: Press Ctrl + Shift + N
• Firefox or Internet Explorer: Ctrl + Shift + P

If this works, you can clear your browser's cache to refresh it. Click this link for the guide: Delete or disable cache and temporary internet files in your web browser.

Please contact our customer support team. To add your account to the list of affected users so that you'll be notified of any updates available through email.

You can also check this article about tracking your customers payments to QuickBooks for reference: Record a customer payment.

If there's anything else I can do for you, I'm always here to help. Take care.