Hi @Karen Pullano!

Currently, there isn't an option to customize your message up to 1000 characters for your customer's invoice.

In the meantime, you can integrate a third party app so you can manually customize a template and add your message for your customer's invoice.

In addition, I'll pass along your request to our product developers. This way, they'll know your need for a customizable message field for your customer's invoice.

Lastly, you can also visit our QuickBooks Resource Center so you'll be updated with all the new features released in our software.

As always, you can visit our Help Articles page for QuickBooks Desktop if in case you need to learn some "How do I" steps.

It'll be always my pleasure to help if you have any other questions. I'll be keeping an eye for your response.