Can I change the message on my invoices at the end of a month or must it be done before new month invoices are created? Why won't it let me change it?

Yes, we can definitely can, bjr09.

I'd like to know if we we're prompted by any error or what happens after we edit a message on an invoice? A browser issue might have caused us not to edit past invoices. Let's use a private browser to verify and see if we can save changes to an invoice. The reason we suggest to open in a private browser is due to it not having stored cache or temporary files as a regular browser does. 

Here's how to open one: 

• Google Chrome: Ctrl + Shift + N
• Internet Explorer: Ctrl + Shift + P
• Mozilla Firefox: Ctrl + Shift + P
• Safari: Command + Option + P

If we were able to do edit it, we can switch back to the regular browser and remove the stored cache files that causes unexpected behavior within QuickBooks. Other browser such as Mozilla Firefox, Google Chrome, and Internet Explorer also have a different cache folders that can also help us get rid any unusual performances. 

You can check out these articles on how to manage your invoice templates: Customize invoices, estimates, and sales receipts in QuickBooks Online.

I'm here if you need anything else. Stay safe!