Cancellations - PHP - Mercado Pago Developers
Which documentation are you looking for?

Do not know how to start integrating? 

Check the first steps

Create cancellation

It is possible to cancel a specific purchase from the payment ID using the SDK below. For details on request parameters, check the Cancellation API.

  $client = new PaymentClient();
  $request_options = new RequestOptions();
  $request_options->setCustomHeaders(["X-Idempotency-Key: <SOME_UNIQUE_VALUE>"]);

  $client->cancel('123456789', $request_options);