Because of an AMEX website update, the Chrome extension on this blog started having issues a couple of days ago and could no longer add offers. We have updated the extension to work with the new AMEX website. The latest extension version is now 1.0.2. If yours still isn't working properly, please check whether the version number is correct.
Extension
After installing this extension, you can go to americanexpress.com as usual to view your AMEX offers. After waiting a bit (it may be slower depending on how many cards you have, so please be patient), a red “Add to All Cards” button will appear under each offer. Clicking it will attempt to add that offer to all of your cards at once.