Building and Organizing Complex Queries-Challenge: Each country's best Customer

Hello friends, please check my code below. It has returned same result in fewer steps. Am I missing some thing??

with customer_country_purchases AS
(SELECT customer.country country,
customer.first_name||’ '||last_name customer_name,
SUM(invoice.total) total_purchased
FROM customer
INNER JOIN invoice on customer.customer_id=invoice.customer_id
GROUP BY 1,2 ORDER by 1,3 )
SELECT country,
customer_name,
total_purchased
FROM customer_country_purchases
GROUP by 1;