in common law systems I know it when I see it is good enough, but I believe most of EU is under a Napoleonic system where you should define what you mean.
i.e. if signup is "email and credit card number" then you're going to be hard pressed to explain why a similar option to cancel does not exist and isn't accessible in as many clicks, with equivalent screen real-estate usage.
So you argue that to cancel a subscription, you should have to provide your credit card number again. If a check on the credit card fails for some obscure reason, you cannot cancel your subscription.
This is what "subscribe is as easy as unsubscribe" also means.