Error when cancelling

Hey, i realize it’s difficult to pinpoint if this is a problem with this plugin specifically, but i’m getting an internal server error whenever i attempt to cancel a subscription (i’m testing it as a normal user, through the “My Account” page).

Since the subscription is actually cancelled in wooCommerce, but not on the PayMill side, i’m assuming that the issue is with the PayMill plugin, though i’m not sure how to confirm this? It just gives me an internal server error after clicking on the cancel, so not a lot of information to go on i’m afraid.

I’m using WordPress 3.9.1, PayMill plugin 1.6.9, wooCommerce 2.1.11 and subscriptions 1.5.4

https://www.ads-software.com/plugins/paymill/