As of April 9, 2018, we have improved our integration with the NMI Gateway in order to better handle the case where back-end processors do not support card validations. These validations are essentially $0 authorizations, and not all processors will accept them.
We will continue attempting to validate the card, but now if the validation fails, we will then try a $1 authorization (which is subsequently reversed.)
Note that the validation or authorization is only done in cases where no payment is due when we are storing a card (a signup to a free product, or a card update for an active subscription). If there is a payment due at signup, or if the subscription is unpaid or past due, then we will not validate the card separately, but will rely on the transaction to tell us whether it is valid.
If this new $1 authorization causes issues for your company, you can skip it by visiting the Settings -> Gateways page, scrolling to the bottom, and clicking the “Disable Card Validation” button.