I appreciate the feedback you've shared, @roomtodiscover.

Let me share some updates about the on-going investigation about your client's inability to open the invoices you've sent (INV-46528). Currently, our Product Engineers are still working on releasing a permanent resolution to this on-going issue.

Rest assured, once there are available updates, you'd be notified via email. Also, it would be applied directly to your account.

On the other hand, you can try viewing the email you've received from our Technical Support team using a private browser or an incognito. This way we can isolate the prompt for a possible browser-related. Here are the shortcut keys you can use:

• Google Chrome, press CTRL  + Shift + N
• Mozilla Firefox: press CTRL  + Shift + P
• Internet Explorer: Press CTRL  + Shift + P
• Safari: press Command + Shift + N

If you’re able to able to successfully view the email, you'd want to clear the cache of your regular web browser. Also, you can use the Browser Health Checkup Tool to check any issues with your browser’s health and its compatibility with QuickBooks Online.

Let me know how it goes in the comment section below if you have other questions in doing your task with QuickBooks. I'm always here to help.