How do I make American Express an accepted form of payment for a sale?

I can definitely walk you through setting up American Express as a payment account for sale, @permianh2osoluti.

The option to accept American Express cards can be added or deleted from the merchant service center. I'll show you the detailed steps:

1. Log in to the merchant service center.
2. Click on Account, then choose Account Profile.
3. Go to Payment Methods, and add Add American Express.
4. Once done, click on Submit.

You'll then see the changes take effect within 3-5 business days.

I'll also attach this module to guide you in making personalization or edits on invoices: Customize invoices, estimates, and sales receipts in QuickBooks Online.

Fill me in if you need extra help with payments or QuickBooks. I'm always ready to assist. Have a nice day and take care!