Custom message upon entering a valid coupon

gistfile1.php

// define the woocommerce_coupon_message callback
function filter_woocommerce_coupon_message( $msg, $msg_code, $instance )
{
    $msg = "Yeah thanks!";
    return $msg;
};

// add the filter
add_filter( 'woocommerce_coupon_message', 'filter_woocommerce_coupon_message', 10, 3 );

thank you!