If I add a TAG to an invoice, does the customer see it?

Welcome to the Community, suefuller66. 

A customer will not see the tags added on an invoice or any other transactions you've sent to them. It's primarily used to let you track transactions however you'd like using customizable label for easy reporting. Also, you can click on Print or Preview option on the invoice as it will show you the information visible on your customer's end. 

Let me share with you this article for your reference: What are tags and why should I use them?

Don't hesitate to reach out to us again or reply below if you have follow-up questions. Have a nice day!