Since you're unable to review your American Express Business card transactions, let's refresh the account to get the data to be reviewed to appear.
The following article contains more information on how to troubleshoot app issues:Troubleshooting Quick-Start Guide for the QuickBooks Online app.
Also, visit this article for more details about the QBO mobile app: QuickBooks Online mobile app feature comparison.
I'm happy to help if you have other questions about QuickBooks Online. Have a good one.