A customer paid $200 on an invoice of $150 i.e. they overpaid $50 on the invoice. 

I sent them a check for $50.

Then followed the Refund Receipt workflow to record the payment of $50 to customer.

But the Accounts Receivables still show negative $50  (-$50) balance against that customer.

Since I already paid back to the customer, the Account Receivable should be zero'ed out.

How do I fix this?