Left Join problem

SELECT CUSTOMER.CUSTOMER,NAME, ISNULL(SUM(SUBTOTAL + TAXES - PAID),0.00) AS BALANCE FROM CUSTOMER  LEFT OUTER JOIN ARH ON ARH.CUSTOMER = CUSTOMER.CUSTOMER  WHERE INVTYPE IN('REG') AND [OPEN] = 1
GROUP BY CUSTOMER.CUSTOMER, CUSTOMER.NAME ORDER BY CUSTOMER

I want to see all the customers and if they have a matching balance then show it. But, it only shows customers with a matching balance?

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