Cancel PMPro subscriptions when a recurring payment fails.

pmpro-cancel-on-billing-failure.php

/*
  Cancel subscriptions when a recurring payment fails. As of PMPro version 1.5.9.1, failed payments reported via Stripe webhook, PayPal IPN handler, or Authorize.net silent post kick off the pmpro_subscription_payment_failed action.
	
  Also make sure to edit the default billing_failure.html email to mention that users are cancelled upon failure. To do so, copy paid-memberships-pro/email/billing_failure.html into themes/{active theme}/paid-memberships-pro/email/ and edit the text to suit your need.
	
  Note: This cancels on the first failure. To cancel only when cancelling at Stripe, see this gist: https://gist.github.com/strangerstudios/5093710	
*/
function my_pmpro_subscription_payment_failed($order)
{
	//cancel the membership
	pmpro_changeMembershipLevel(0, $order->user_id);		
}
add_action("pmpro_subscription_payment_failed", "my_pmpro_subscription_payment_failed");