functions.php

<?php
add_action( 'woocommerce_applied_coupon', 'change_subscription_next_payment_due_date' );
add_action( 'woocommerce_removed_coupon', 'change_subscription_next_payment_due_date_on_remove_coupon' );

function change_subscription_next_payment_due_date( $coupon_code ) {
	if ( 'famille' === strtolower( $coupon_code  ) ) {
		replace_recurring_price( $coupon_code, 'add');
	}
}

function change_subscription_next_payment_due_date_on_remove_coupon( $coupon_code ) {
	if ( 'famille' === strtolower( $coupon_code ) ) {
		replace_recurring_price( $coupon_code, 'remove' );
	}
}

function replace_recurring_price( $coupon_code, $what = 'add' ) {
	if ( did_action( 'wp_loaded' ) && isset( WC()->cart ) ) {
		$contents = WC()->cart->get_cart();
		$coupon = new WC_Coupon( $coupon_code );
		$amount = $coupon->get_amount();
		if ( ! empty( $contents ) ) {
			foreach ( $contents as $item_key => $item ) {
				$product = $item['data'];
				error_log( print_r( $product , 1) );
				if ( ywsbs_is_subscription_product( $product )  ) {
					$subscription_info = $item['ywsbs-subscription-info'];
					if ( $subscription_info ) {
						$price = $what === 'add' ? $product->get_price() + $amount : $product->get_price() ;
						WC()->cart->cart_contents[ $item_key ]['data']->set_price( $price );
					}
				}
			}
		}
	}
}