Hello. I am a Japanese user and live in Japan.
I purchased STH-ETH-250 from an US seller through ebay.com.
I connected it with Ethernet cable and its lamp is flashing(green).
But on SmartThings app, it is offline and cannot connect even if using code.
What should I try to do?
Flashing green light on the hub indicates that the hub is looking for devices to connect with, if the app is showing hub as offline try to uninstall and reinstall the app that might help you
If it was me - I would return the item and get your money back. In the past, the US hubs were extremely difficult to set up for use in foreign countries. If you did want to use a v2 hub, I would look for the one that was released for the Asian Pacific region.
I would recommend that you look for an Aeotec Smart Home Hub for SmartThings or the Station if you are are not looking to use z-wave devices. The Station would be a much lower cost but I am unsure what regions it is available.