2Checkout Purchase does not get added to Subscription

When a user on my site purchases a subscription using the 2Checkout gateway, the payment goes through, but that user is never added as a member of that subscription. I also use Paypal as a Gateway and users who pay via Paypal have no problem, they get added to the subscription as soon as they pay. Please guide me as to what I might be doing wrong, or if this could be a bug with the plugin? Thanks!