Hi there slkidsclub,
Thanks for reaching out about your customer's contact information. QuickBooks Online is a great tool able to assist you in creating and sending invoices to your customers so they can know the amount owed for your services. I can provide information about adding a secondary email for your customer.
To add another email so transactions are sent to two emails, go to the Sales tab, then Customers section. Click on the customer in question, then Edit. In the email text box, beside the first email, add a comma, then a space, and then the second email. Don't forget to save.
If you have any other questions, feel free to reach out here.
