First things first, we should note that in QuickBooks Online, once the customer pays a sales receipt, they recognize it as Paid. If your member's credit card gets declined/denied after, you should see a reminder on the Homepage: Take Action - Fix declined credit card payments.
According to QuickBooks, to exclude a declined customer credit card payment:
Go to Transactions > Banking.
On the For Review page, select the customer payment.
Click the Batch Actions button and click Exclude Selected.