Mobile apps for 90 days reporting are no longer available in official stores, Apple or Google, for a quite while. Not sure that server error is because of that. The current system is on web browsers (
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Better to go to the immigration bureau site and click TM.47 link from the top page to see the notification on the popup window at least for the first time. (
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Your options 2-a) or b) would work, too. Your choice.