How do I change the customer email address for invoicing

You have options on where to change the customer's email address shown on the invoice, tstoreysfa. 

First, if the email address is a new permanent one, you can change it in the customer's profile. Let me show you how:

1. Go to Sales from the left menu.
2. Click Customers. 
3. Look and select the customer's name. 
4. Click the Customer Details tab, and click the Edit button at the middle-right of the window. 
5. Change the customer's email under the Email field. You can also add it as another email by adding a comma to separate multiple emails. 
6. Click Save. 

Second, if this is a temporary email that is just applied to the specific invoice, you can open the invoice again and change the email form there. Then, Save and send. 

You can also look into all your list of invoices to check the email status. Still from the Sales menu click Invoices. Under the STATUS column the email status is enclosed with a parenthesis. 

If you have further questions, I'll be here to help!