Undefined index: s2member_paypal_xco

Hi, I’m trying to test on the real paypal upgrading from a free membership to a paid membership. I have sucessfully tested purchasing memberships in the past and they have gone through fine. When I try to upgrade, I’m able to purchase it just fine, but I’m getting a notice. I’ve check in paypal and it looks like the payment has gone through. This is the notice I’m getting:
Notice: Undefined index: s2member_paypal_xco in /home/napkinma/public_html/dev/psg16/wp/wp-content/plugins/s2member-pro/src/includes/classes/gateways/paypal/paypal-checkout-pf-in.inc.php on line 328

How can I resolve this?

Thanks,
Jason