Can customer pay 3 invoices with one online payment. How?

Welcome to the Community, @Wende

Currently, allowing customers to pay multiple invoices at one time isn't possible in QuickBooks Online Payment. However, third-party applications are available that allow customers to pay as many invoices as they like. You may check this link to find the best app that suits your business needs: QuickBooks app.

You may want to apply one payment to multiple invoices through another payment method you can place a checkmark to the left of the invoices on which you want to apply the cumulative payment amount received.

Here's how:

1. Go to the Customers menu, then Receive Payments.
2. Select the customer under the Receive From dropdown.
3. Enter the payment date, amount, and payment method.
4. Checkmark the invoices which you want to apply for the payment.
5. Once done, hit Save.

I've included this article for more details: Record an invoice payment.

For future reference, check out this article to learn more about receiving and recording invoice payments.

Feel free to reach out again, if you have further questions about another method of paying 3 invoices by customer or other QBO-related concerns. I'll be happy to assist you.

@WendeWoolley 

You can use a 3rd party merchant service to do so. Another option, ask your customer to signup for a free billing management app as a workaround. They can pay you with ACH or Check for free.