Hi there, Crystal. The option to add a secondary payer directly in QuickBooks Online is not available. However, I can provide you with some workarounds to manage their payments effectively.
While there's no option, you can add another email address when creating the invoice. This way, both of your customers can receive the invoice, and it's up to them how much they'll pay.

Additionally, you can get a payment link for the invoice and send it to your customers. Here's how:
- Hover the +Create button on the left side panel.
- Select Payment links.
- Choose the Multi-use payment link option.
- Enter the necessary information, then click Create link.
- Copy the link, then send it to your customers through email or social media.

If you still have other concerns related to QuickBooks, don't hesitate to reply. We're here to help.