Hello there, @Tdroe.
When deactivating an account (American Express) in QuickBooks Desktop (QBDT), you need to make sure there are no pending transactions and the last connection has been completed. Since your account is already updated, you can re-sort your list to go back to its default order and remove the error message you've encountered. But before doing so, you'll have to make sure you create a backup of your company files.
Once ready, here's how:
- Go to the Lists menu,.
- Select Chart of Accounts.
- Click the Include Inactive checkbox. If it's grayed out, there are no inactive names.
- Go to the View menu, then select Re-sort List.
- Select OK.
- Close and reopen your company file.
In case the issue persists, I'd recommend performing Solutions 2 and 3 in this article: Fix issues when deactivating bank feeds.
When everything is all set, you're able to deactivate your account. Just make sure to add or match any American Express pending transactions. Then, follow the steps below:
- Go to Lists from the top menu.
- Select Chart of Accounts.
- Locate and right-click the account (American Express) you want to deactivate.
- Choose Edit Account.
- Go to the Bank Feed Settings tab.
- Select Deactivate All Online Services.
- Click Save & Close.
- Hit OK to confirm.
I've attached a screenshot below that shows the fifth to seventh steps.

After that, your new transactions won't download. When the lightning bolt disappears beside the account this indicates it's already deactivated.
When you're ready to reactivate your American Express account, kindly refer to this article for the step-by-step guide: Set up bank accounts for Bank Feeds. It provides two ways to connect your account to bank feeds (Direct Connect and Web Connect).
Once reconnected, your new transactions will be downloaded. With this, you'll have to add and match them to keep your account accurate and updated. For the detailed steps, you can check out this article: Bank Feed transactions. It includes instructions about reviewing transactions based on the banking mode you're using.
You can always drop your comment below if you have other concerns or follow-up banking inquiries in QBDT. I'm just around to help. Take care always.