How do I save and show the credit card fee on the order page. When I get the response from the gateway I too get the credit card fee amount but it's not being added to the order and isn't viewable anywhere - does anyone have any experience with that?
I would save the response to an incognito field (or fields) on your order (probably both the entire response and also just the fee separate out).
The readonly incognito field is particularly good for this sort of thing - I use a bunch of these fields in a debug tab on my order layout to save useful things.
Just create the fields, add the fields to your order, and you update the values with the usual
<input name="fields[fieldName]"> syntax with any cart operation, or use
setContentFromPost if you're in a plugin:
$order->setContentFromPost(array( 'fieldName' => $creditCardFee, )); craft()->commerce_orders->saveOrder($order);