I think you are banned from participating open chat. I'm not sure but if a user adds too many friends or opens many open chats in short period, or If user's number is overseas virtual number(I don't know if it is the right term but like if your number is not indentifiable), then it happens. But It is not permanent, may be several weeks at the longest. If you didn't and won't do anything that violates kakao policy, they will eventually let you join open chats. Sorry.