I can see the importance of being able to connect AMEX Business Checking to QuickBooks. I'm here to share some information so you'll be guided on what to do, blanders.

The American Express is available under Open Banking. Normally,  you'll just have to make sure you're using the correct URL when searching for the bank. To do this, follow the steps below:

1. From the Banking menu, select Connect account.
2. Enter the bank's URL.
3. Look through the results to find your bank.

However, if you can't find the URL on the list, I suggest requesting support from your bank. Here's how:

1. Go to the Banking page and select Add account.
2. Search for the name of your financial institution. If QuickBooks is unable to find your bank, you'll get the message, "Hmm, we can’t find [name of the bank you entered] in our list of supported banks," and you'll be given tips to locate your bank.
3. Select the Request support for your bank.
4. Enter your bank's name and web address (URL) in the field provided, then select Request.

Furthermore, you may want to manually upload transactions in the meantime while you're still unable to connect your account. Go through this article for more details: Manually Upload Transactions In QuickBooks Online. 

Please touch base with us if there's anything else that you need about connecting accounts. The Community is always here to help you 24/7.