I appreciate you for sharing the details of your concern as well as the error message you received on your end, @Longtimer556.

I checked here on my end and found no reports of a problem with the Payments Links in QuickBooks Online (QBO). Rest assured, I have some suggestions for how we can solve this problem.

The 404 error simply indicates that the web page you are attempting to access could not be reached or was not found on the server. To isolate this, I recommend accessing the payment link from your QBO account in an incognito or private window.

This allows us to determine whether the problem is due to browser caching. Too much data stored from the browser causes inconsistencies that affect your account's performance. Using a private window helps to verify the issue as this doesn't save any data.
 

To open a private window, you can refer to these keyboard shortcuts: 
 

• Ctrl + Shift + N for Google Chrome browser
• Ctrl + Shift + P for Mozilla Firefox & Microsoft Edge browsers
• Command + Shift + N for Safari browser

If you can access the Payments Links menu, I recommend clearing the cache in your default browser to refresh the system. Using other supported browsers also aids in narrowing down the problem.

Once you're ready, here's an article to help you match your online payments and invoices to avoid duplicate entries: Categorize and match online bank transactions in QuickBooks Online.

Do you require additional assistance with managing your invoices and online payments? Please do not hesitate to include them in your response. I'll be right there to help you whenever you need it!