Lots of good advice.
I’ll just add that Amex Offers are targeted to individual cards (both primary and AU can get them, and an AU might get an offer that the primary doesn’t get, or vice versa, and sometimes both primary and AU will get the same offer). Amex Offers can be widely available or very narrowly targeted. For really popular Amex Offers like Samsclub, Staples,
Best Buy, Lowe’s, Home Depot — basically places where you can redeem the Amex Offer by buying gift cards — it’s best to add them to your card ASAP, because some offers do “fill up.” You just have to check the offers tab on each card.
Each Amex card (primary or AU) can sign up for its own Amex online account, but you can add more Amex cards to existing accounts if that makes it easier to manage your cards. However, Amex Offers are usually limited to 1 per online account. So like
@platamama said, say you have more than 1 card on your Amex account, and you got the Sam’s Club offer on, say, 3 Amex cards, once you click to add the offer to 1 card, that offer will disappear on the 2 other cards it was on. Adding an Amex Offer to a card on your login will not make the Offer disappear on DH’s card if DH’s card is on another login.
You can get around this limitation by opening up new tabs or windows for each of your cards, go down to their Offers, and click to add the same offer in the different tabs or windows.
@calypso726 wrote up a good guide (with pictures) showing you how to do this:
https://www.disboards.com/threads/i-love-credit-cards-so-much.3528202/page-897#post-58922317
P.S. you always refer to your card as the AMEX. I’m guessing that’s your Platinum, but it would really help us keep our advice straight if you tell us what Amex you’re referring to, especially as you get more Amexes.