The correct URL construction is
https://api.twitch.tv/helix/streams?user_id=26610234&user_id=567803342
You might have to use not params and string concantenate the URL instead
payload = {‘user_id’:‘user1’,‘user_id’:‘user2’…}
Creates and object of only on entry
payload = {‘user_id’:[‘user1’,‘user2']}
Make work but I’d not to familair with Python.
So building the URL manually instead of using params might be the way to go