The error may appear when there's an issue with the browser. This is the reason why you're unable to add more than three email addresses in the CC field.
However, we can perform some basic troubleshooting steps to quickly address the issue. This way, you can get back to your business and send your invoices to your customers.
To start, use a private browser to access your account in QuickBooks. It is also known as InPrivate in Internet Explorer and Incognito mode in Google Chrome. This browser mode doesn't record the browsing activity on your local device. You can access this by pressing the following keys:
Ctrl + Shift + N (Google Chrome).
Ctrl + Shift + P (Firefox).
Control + Option + P (Safari).
If you're able to add a multiply email address to the CC field, then let's clear the cache in your web browser or try using a different supported browser. This can be a temporary issue with QuickBooks and the current browser that you use.