Adds a new subscription position on the checkout before the submit button.

mailpoet-subscription-positions.php

add_filter('mailpoet_woocommerce_subscription_position', 'wc_mp_before_order_button');

function wc_mp_before_order_button( $subscription_positions ) {
  $add_subscription_position = array(
    'review_order_before_submit' => __('Before Order Submit')
  );

  // Add the subscription position.
  $subscription_positions = array_merge($add_subscription_position, $subscription_positions);

  return $subscription_positions;
}