Whenever you try to make a payment, we submit the charge to the bank for approval. Your bank then decides whether or not to accept this charge from us.
American Express is historically cautious when it comes to accepting purchases, so it happens more often with them.
You may also get a notification from American Express flagging your Karma purchase. You’ll want to contact American Express to allow the purchase to go through.
If you have a MasterCard or Visa on hand, you might want to try that instead. They’re a little less cautious.