Keep subscription active when order is paid for via SEPA. Works with parent and renewal orders.

wcs_sub_active_SEPA.php

<?php
/*
 *
 * Keep subscription active when order is paid for via SEPA.
 * Works with parent and renewal orders.
 *
 */

add_action( 'woocommerce_order_status_changed', 'wcs_sub_active_SEPA', 10, 4 );

function wcs_sub_active_SEPA( $order_id, $status_from, $status_to, $order ) {
    if($order->get_payment_method() === 'stripe_sepa' && $status_to === 'on-hold') {
        if ( wcs_order_contains_subscription( $order, 'any' ) ) {
            $subscriptions = wcs_get_subscriptions_for_order( $order, array( 'order_type' => array( 'any' ) ) );
            foreach( $subscriptions as $subscription_id => $subscription ){
                $subscription->update_status( 'active' );
            }
        }
    }
}

/*
 * uncomment to calculate 'Next payment date' based on last renewal order creation date, 
 * NOT the date payment was actually received
 */
//add_filter( 'wcs_calculate_next_payment_from_last_payment', '__return_false' );