Change or add parameters to the name-value-pair string sent to PayPal’s Payflow Gateway when processing a subscription cancellation. Passes the $nvpStr and order object.

apply_filters( 'pmpro_payflow_cancel_nvpstr', string $nvpStr, MemberOrder $order );

Parameters

$nvpStr

string; A URL-encoded name-value pairs for the request and response fields of the cancellation

$order

object; A full MemberOrder object

Source

File: https://github.com/strangerstudios/paid-memberships-pro/blob/master/classes/gateways/class.pmprogateway_payflowpro.php