All implementation must implement the Reverse endpoint for transactions that alter a card's balance. In the past we considered this to be optional, but through experience we learned that any integrators who did not implement this inevitably ended up with scenarios where they did wish to undo transactions but were unable to do so.
It should be noted that our Connect Manager portal does not provide the capability to undo a transaction – this can only be done via our APIs.
It is up to the integrator whether they wish to allow customers to reverse their own transactions, or whether to limit this functionality to administrators who can handle these scenarios on a case-by-case basis