I need to find a way to remove a user from my slack team without having a paid version of slack.
I found this API method: users.admin.setInactive
But it requires me to have a paid version. Are there any workarounds to make this possible on a free tier Slack?
No. Unfortunately, deactivating a user by API is only possible with a paid version of Slack.
But I can offer a few organizational workarounds from my experience with managing large Slack teams on free tier that makes work easier for admins:
Automatic removing from private channels
You can still programmatically remove users from private channels. So one workaround is to structure your Slack in a way, that all important channels are private. Then you have a batch running that automatically removes users from those channels when they fail to meet a defined criteria.
Automatic notification of users to be disabled
Have a batch running that is automatically notifying you / the admins about any user that fails to meet your defined criteria and need to be disabled. Then you still need to disable them manually of course, but you can be sure to be informed timely and that you don't miss anyone.