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action is not described

woocommerce_applied_coupon action-hook . WC 1.0

Usage

add_action( 'woocommerce_applied_coupon', 'action_function_name_9620' );
function action_function_name_9620( $coupon_code ){
	// action...
}
$coupon_code
-

Where the hook is called

WC_Cart::apply_coupon()
woocommerce_applied_coupon
CartController::apply_coupon()
woocommerce_applied_coupon
woocommerce/includes/class-wc-cart.php 1791
do_action( 'woocommerce_applied_coupon', $coupon_code );
woocommerce/packages/woocommerce-blocks/src/StoreApi/Utilities/CartController.php 850
do_action( 'woocommerce_applied_coupon', $coupon_code );

Where in WP core the hook is used WooCommerce

woocommerce/includes/class-wc-cart.php 107
add_action( 'woocommerce_applied_coupon', array( $this, 'calculate_totals' ), 20, 0 );