There is an ongoing investigation about invoices not being sent to clients, sarah-peet-mercu.
Our product engineers are still investigating to check the cause of the issue so they can look for a permanent fix. I'd encourage you to give us a call so we can add your account to the lists of affected users.
Here are the steps:
- Click the Help icon in the upper-right corner of the screen.
- Select the Search tab and tap Contact us.
- Enter a brief description of your concern, then click Continue.
- Choose a way to connect with us.
As a workaround, consider downloading the invoice and then sending them to your clients outside QuickBooks Online.
You can also use this article for other troubleshooting steps in resolving the issue: 3 solutions for you when customers aren't receiving your emails.
It'll be my pleasure to help if you have other concerns.