I was working in the Core API Explorer this morning, trying to get the GPA balance for a business user. I had trouble finding the endpoint because the /balances endpoint was listed under "cardholder balances." The description says "Operations for cardholder balances." That doesn't sound right to me. Balances are available for any GPA, whether that's a user or a business. It applies to more than just "cardholders" since "a business is a type of account holder that cannot directly hold cards."
