This error message is indeed a bit weird, because if the scopes are wrong it simply tells you “Missing scope” in the reasons. If the key in general is incorrect it will tell you “Invalid session”. So this specifically sounds like an issue to call the endpoint and not like a problem with the key.
What homey are you using and which version are you on?
When you go the the homey developer page Web API playground and try to run Homey.thread.executeCommand({ command: 'leaderdata' }) does that work?
