How do I process a client's credit card payment in Quick Books Online?

I'm glad to see you here in the Community, @cbaliko.

Let me guide how to process your client's credit card payment in QuickBooks Online. 

To start, we'll need a QuickBooks Payments account to process credit cards in QuickBooks Online. If you don’t use QuickBooks Payments, you can record a credit card payment you processed outside of QuickBooks.

There are two ways to process card payments with your account. 

The first option is to receive payment towards an invoice. I'll show you how:

1. Select the +New button and then choose Receive payment.
2. Enter the customer's info and payment date.
3. Choose an open invoice to apply the payment under the Outstanding Transactions section.
4. From the Payment method drop-down menu, choose Credit card.
5. Select Enter credit card details and then fill in the credit card info.
6. Click Process credit card and then choose Save.
7. Once done, click Save and close.

However, if you don't use invoices, you can process a credit card with a sales receipt. 

Here's how:

1. Click on the + New button.
2. Choose Sales Receipt, then enter the customer's info.
3. Add a product or service to sell.
4. From the Payment method drop-down menu, choose Credit card.
5. Choose Enter credit card details and input the information.
6. Select Process credit card and then click Save.
7. Once finished, choose Save and close.

I've added this reference that can guide you in accepting customer payments for online invoices: Take and process payments in QuickBooks Online. Through QuickBooks Payments, you can process payments right in QuickBooks Online.

Let me know if you have further concerns. I'd be glad to assist you. Have a pleasant day.