revoke-trial-access.php

<?php

function subscription_stopped_func($event) {
  $sub = $event->get_data();
  $latest_txn = $sub->latest_txn();

  if ($sub->in_trial() && $latest_txn) {
    // Set transaction's expiration date to yesterday. Effectively revokes their membership access.
    $latest_txn->expires_at = MeprUtils::ts_to_mysql_date(time() - MeprUtils::days(1));
    $latest_txn->store();
  }
}
add_action('mepr-event-subscription-stopped', 'subscription_stopped_func');