'Housespicyramen' having difficulty joining the Naver cafe made me think that this issue might be more common than expected. I'm sharing this in case there are more international members who hasn't transitioned to Naver cafe.
Naver is primarily a Korean domestic service and never (naver?) was architected with foreign users in mind, and Korean internet service tends to emphasize the verification of identity in general. This particular online culture could make it tricky for a non residents in Korea to join a domestic service and an attempt for joining from outside of Korea triggers 'suspicious' activity flag a bit too easily. This is especially ironic because one of the reasons why this fan club eventually settled at Naver (instead of Daum) was easier access. Go figure.
So can you as a non Korean join Naver? - Yes!
They allow foreigners who live in or outside Korea to join Naver albeit in a limited capacity. But is it simple and easy? Nolt necessarily. Because of high security sensitivity they tend to block even legitimate attempt to join as malicous activity.
Why do you get flagged as a suspicous user?
Fair or not this unfortunately is the current state. Again Korean services aren't geared toward non Korean users and their security measure is overly senstive (and dumb), so don't take it personally if you get flagged as a hacker trying to break in. (Unless you really are a hacker, but then you wouldn't be reading this ;)
Can you appeal and get through this hurdle? - Yes!
It involves a maunal way to provide a proof that you are a real person, using a government issued ID. It is a hassle but thankfully they don't require you to use fax so that's a relief ;-) Below is the link to request lift on restriction if you have one on your account.
https://help.naver.com/inquiry/input.help?categoryNo=18202&serviceNo=5640&lang=en
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네이버 서비스 이용에 필요한 고객센터 도움말을 확인해 보세요. 검색과 스마트봇으로 더욱 쉽고 빠르게 궁금한 점을 해결할 수 있습니다.
help.naver.com
Gemini suggests that you only provide minimal information of your identity and redact more senstive personal data, which I think is smart thing to do.
After submitting your ID it will take a few days for them to manually verify it and lift restrictions.
I am a Korean but I live abroad so I had some inconvenience joining the service like 20 years ago. I remember that the process was more complicated but at the same time the security wasn't as overly senstivie. Good luck joining this myoptic internet service in order to join the current official Dorado fan club, until they expand to the service platforms more adequate for the global fandom.