Hello there, @JRamirez2. 

Thank you for posting here in the QuickBooks Community. I appreciate you for performing the steps to change the email address. 

You have the email but can't populate the email address. Check if it has anything to do with the browser you're using. Your browser's cache saves your data. 

• Google Chrome: Ctrl + Shift + N
• MS Edge and Firefox: Ctrl + Shift + P
• Safari: Command + Shift + N

If your invoice auto-populates your customer's email addresses, you can go back to your regular browser and clear its cache. If not, please try other browsers to see if we get the same thing. 

Also, you can still follow the steps provided by my colleague, MaryLandT, to set up the email address on the customer profile. 

If none of the steps will fix the issue, I recommend contacting our QBO Support to check this further using more tools. 

If you need to send numerous invoices, go to the Send multiple invoices page. You can also send clients reminders when their invoices are past due.

You can always leave a comment below if you have follow-up questions about your business data. I'm continuously here to assist you. Take care.