Question about Subscriptions

[Bruno]

Hello,

There is some new Literary magazine that has been receiving many requests in the 'Add new books' section.

Some of these requests have been closed without adding with the reason of 'being a subscription magazine'.

So I'm requesting some clearing about what Subscription means here. Maybe there's some language difference.

In Portugal, books available by subscription mean that we pay a timely fee (once every month, 3-month, yearly, ect) and while we're paying that fee, we are receiving the books.
If we want to buy one particular book, and not the rest, we can not do that as the book isn't available for a single purchase.

That doesn't seem what is happening with this Volume 0 magazine. Looking at their page:
https://www.volume0.com/stacks

It seems to me that we can buy the items separatelly.
When trying to buy a single issue, we go to a page that states 'Faturação da Assinatura' which translate to something like Signature(subscription) payment, but I don't see any sign that anything more than the price of the single issue (20 US$) will be charged.

Also, I see that previus issues were already turned Invalid, but Issues 4 and 5 were added by GR Staff (not much of a point, as they have done mistakes in the past, but still a point):
https://www.goodreads.com/book/show/2...
https://www.goodreads.com/book/show/2...

So I'm asking for some clearing so I can understand how to act on this magazine, and in similar questions in the future.