2checkout gateway suddenly stopped working

I’ve been using Membership and the 2checkout.com gateway successfully for about two months. My last two signups had problems. Other signups earlier in the day worked fine.

Specifically, the user account wasn’t activated with a subscription. When I look at the 2checkout.com website, the payment was completed successfully. However, the transaction doesn’t show in Membership => Payment Gateways => View Transactions.

Please help!