Thank you for posting here in the Community, @info295.
I can show you how to enter multiple email addresses for a single customer in QuickBooks Online. Please start by visiting the profile to add the information and separate them using a comma.
After following the steps above, customer email addresses will automatically show when creating an invoice.
For additional reference, I've attached an article you can use to customize invoice emails, as well as the option to choose Full details or Summarised details: Customise your invoice emails.
If you have additional questions or concerns while working in QBO, leave a comment below. I’ll be happy to help you out.
Thank you. I tried semi colon but that didnt work!!!