Not to say you’re wrong (I seriously have no clue), but how many people in Japan use Capital One / AmEx tho? They might not put their nose where there’s no volume either. For what it’s worth, AmEx is often not accepted where I live. I wonder if it is the same over there?

Just to make sure, your issue is :

But I cannot access https://audiobookshelf.local.com/ or http://audiobookshelf.local.com/ (it automatically forwards to HTTPS).

If so, well, you’re forcing SSL, which means it’ll automatically transmit http request to https. If you don’t want that, turn it off. Anyway, it’s going to be used only locally, correct?