How do I turn off online payment option for one customer?

Glad to have you here in the Community, @kelseyhutchinson.

We can change the customer's payment into a check in QuickBooks Online (QBO). This way, the online payment option will turn off.

Here's how:

1. Go to the Sales menu, and then choose Customers.
2. Locate a customer you want to edit and click on their name. 
3. Under the Customer Details tab, click on Edit.
4. On the Customer Information window, go to the Payment and Billing tab.
5. Select the Preferred payment method drop-down arrow, and then choose Check.
6. Click Save once done.

You can also uncheck the payment method under the Online payments section on each transaction when sending it to the customer.

You might want to read this article to learn about online payments: QuickBooks Online Payments.

Please keep in touch with us here in the Community should you need any further assistance. I'm always here to help.