It always updates my user profile instead of the user that I specify in X-Slack-User:
https://slack.com/api/users.profile.set?token=yadayadayada&X-Slack-User=XYZ23456&Content-type=application/json&charset=utf-8&profile={"status_text": "Test #1","status_emoji": ":gb:","status_expiration": "5"}
The user Ids that I tried to specify are valid ones, I'm an admin and I created an app with the required rights, the legacy token did no good as well, this works, but just for my user, X-Slack-User is not working in my case.
I'm on a free plan so passing "user" as a param doesn't work for me, as states the API: "ID of user to change. This argument may only be specified by team admins on paid teams."
Is there maybe another way to update the status of other users on a free plan Slack?
As you already stated the API method users.profile.set can only be used to change the profile of other users if you are an admin and on a paid team. A property X-Slack-User is not part of the API, so it will not work either.
There is a workaround for teams on a free plan tough:
The API method will always work to change the profile for the owner of a token. You could collect tokens from all you users and then use those to change the status for each user. For that each user will have to install your app though OAuth once. This will create individual tokens for each user, which your app needs to store. This is called "configurations".