Trying to reconcile my Amex account - 2 cards are linked to one account, but transactions are only pulled in for 1 card. How can I bring in transactions for both cards?

I'm here to provide the appropriate way of reconciling your Amex account with two cards linked to it, @nikkiboucard. 

We receive the data on how your bank sends the downloaded transactions to QuickBooks Online (QBO). This may be the reason they are pulled in for one card. 

When connecting the accounts to Online Banking, you're unable to connect both parent and its subaccounts. I'd suggest contacting your bank to confirm how they send the downloaded transactions. If these download to your Amex main account, connect only the parent account. If these go to the two cards, connect only the subaccounts. For more information, see the Connect the accounts to Online Banking section through this article: About Bank or Credit Card Subaccount Setup. 

Once done, you'll only need to reconcile the parent account. It's because all transactions from the two cards roll up into it. I recommend having your Amex statement handy before performing the steps below. 

1. Go to Accounting from the left menu. 
2. Select Reconcile. 
3. Choose the Amex main account from the Account drop-down menu. 
4. Review the Last statement ending date. 
5. Check the Beginning balance.
6. Enter the Ending balance and Ending date. 
7. Click Start reconciling.

For the detailed instructions, check out this article: Reconcile An Account. 

As always, you can visit this resource hub: Reconcile Workflow. It provides you more details about starting, fixing any differences, and completing the reconciliation process. Just click the links beside QuickBooks Online. 

Please know that I'm around to help if you need further assistance. Enjoy the rest of your day, @nikkiboucard.