Welcome to the Community space, crawf. Allow me to assist you in how to process credit card payments on your invoices in QuickBooks Online (QBO).

You can enable the option of credit card payment on the invoices using QuickBooks Payments. This payment process can help you accept and manage client's invoice payments. To proceed, you'll need to sign up for QuickBooks Payments first:

1. Sign in to your QBO account as an admin.
2. Go to the Gear icon ⚙, then select Account and settings.
3. Select the Payments tab, and from the QuickBooks Payments section, click on Set up payments.
4. Fill out the information needed on the signup window.
5. When you completed all of the sections, select Get Set Up.

After that, you'll get an email notification regarding your QuickBooks Payments enrollment after a few business days.

Additionally, you'll need to set up your QBO account settings so your clients will know that they can pay invoices through a credit card online. Here's how:

1. Go to the Gear ⚙ icon, then select Account and settings.
2. Select the Sales tab.
3. Under Invoice payments, click Edit, then choose the payment options you want. You can also enter your Payment instructions, which will show on all invoices you create.
4. Click Save and Done.

Also, you'll need to set your payment directly on the invoice you create. 

1. Go to the Sales tab, and select Invoices.
2. Locate the specific invoice, and select Edit.
3. Choose the Payment methods.
4. Turn on or off the switches for the payment method you'll use.
5. Click Save and close.

For step-by-step guidance, you can refer to this article: Take and process payments in QuickBooks Online with QuickBooks Payments.

Furthermore, you can check out this article to learn how to process a refund for your clients or invalid payments: Void or refund customer payments in QuickBooks Online.

I'll be around if you have further assistance regarding invoice payments or other QuickBooks-related concerns. I'll be happy to serve you. Keep safe.