Different accounts are in different “shards” in the SmartThings cloud, and so have different URLs.
When posting to the forum, it is best to use the universal sign-on link,
https://account.smartthings.com
Which will work for anyone since it automatically redirects you to the correct shard for your account.
Otherwise people can get very confused and even cause some problems for themselves if they start working on a shard which is not associated with their account.
See the community FAQ:
When SmartThings went for sale in the UK, they added the first of what will be many “shards” to split the SmartThings Cloud workload into multiple, somewhat independent, clusters of servers.
SmartThings automatically replicates a lot of stuff between the shards when they deploy updates and so on, but if you are doing development and you Publish “For Me”, then you need to be sure to be logged into the correct shard, or your self-published SmartApp or custom Device Type Handler will not work. You won’t find it in the mobile App!
Eventually you may not need to know your shard. Eventually, SmartThings may make this process automatic and when you self-publish, it will go to the “right” shard without intervention.
Update:
The URL: https://account.smartthings.com should take you to your correc…