Your points balance will show as negative if you refund a purchase but the Loyalty points you earned for that purchase have already been removed from your account and converted into a Loyalty reward voucher.
Once points are in the process of becoming a voucher, we are unable to cancel the voucher. Therefore, you'll receive the Loyalty Voucher and the points equivalent to the refunded amount will be deducted from your account. As you continue to earn points, the negative balance decreases.