QBO: How to send existing invoices to multiple customers

On your dashboard, click the "New" button on the top of the sidebar, and select "Request: Send an invoice"

"Send invoice(s) awaiting payment" to see a list of all outstanding invoices from all customers.
Please note that by default, since this view is for multiple customers and meant for bulk processing, you won't be able to select which contact at each company you want to reach. If that's important to you, check out this link instead.

Check the invoices that you want to pay, as well as the bank account you want all funds to be deposited to, and select "Send invoice".
That's it! You're good to go.

Seeing this red alert? Match your customers from QBO to Routable, and you should see all existing invoices show up here.