Cannot connect my American Express (AU) account no matter what I try I get error try again in a few hours (0591) - any problems for others?

I appreciate you for reporting the problem you encountered with connecting your American Express (Amex) AU account to QuickBooks Online (QBO), Benjamin. 

I'm here to help troubleshoot why you can't connect your Amex AU account to QBO. 

Here are some things that need to be checked first: 

• If you use the American Express - Connect to QuickBooks app will only support one (1) connection to one (1) QuickBooks Online company.
• If you manage multiple OPEN credit cards for multiple companies under one (1) Amex login, the user will only be able to connect the Amex account to one (1) QBO account for it to work properly.
• If the user manages multiple OPEN credit cards but accesses them by using different Amex logins, the user will need to connect the additional Amex OPEN accounts through the standard Bank Feeds connection for American Express.

After taking into consideration the things stated above, you can follow these steps to troubleshoot your banking connection: 

1. Sign in to your Amex account's website. (You can find the link from the time link your account to QBO.)
2. Check your account for messages, notifications, or alerts.
3. Look for any display issues as you navigate the website. These can block QuickBooks from connecting with your account.
4. Check your bank’s website for any announcements about new security requirements.

If you haven't found any issues, proceed with connecting your Amex account. To ensure everything works as expected, I'd recommend accessing your account through your browser's incognito mode and connecting your Amex from there: 

• Google Chrome: Ctrl + Shift + N
• Microsoft Edge: Ctrl + Shift + N
• Firefox: Ctrl + Shift +P
• Safari: Shift + Command + N

Once you have opened the browser window, log in to your QuickBooks account and see if you can connect your Amex account. If you can, proceed to clear your browser's cache. This process will remove and fix specific issues and help the program run optimally. Additionally, you can use other devices and supported browsers. 

Let me add this article about categorising your transactions in QBO as a future reference: Find, categorise, and edit transactions in QuickBooks Online. 

We'll be here in the Community if the error you experienced with connecting Amex to QBO persists. We'll do our best to assist.