How can customers who don't register view their subscription?

Every customer who places a subscription order in your shop (whether registered and logged in or not), can view and edit the subscription through the so called "magic link" which is contained in every subscription e-mail. This magic link authenticates the authorized user and allows the subscriber to edit the subscription without having to log into their account. These links are always present in the subscription e-mails. You (the merchant) can view this link if you go to your App settings -> Subscriptions -> click on a subscription -> Access customer portal.