Check your logs/private-messages directory and after running the host command, check the latest log and look for what is replied. You might need to add the bot as a Channel Editor to your channel on your Dashboard, on top of the original verification to get the API key.
Example, this is with my test bot not having Channel Editor access on the Dashboard:
[09-21-2017 @ 22:00:03.024 MDT] jtv: you don't have permission to perform that action.
This is after giving the bot Channel Editor:
[09-21-2017 @ 22:06:55.769 MDT] jtv: now hosting illusionaryone.
[09-21-2017 @ 22:06:55.771 MDT] Received a start host mode notification on user illusionaryone from jtv
[09-21-2017 @ 22:06:55.774 MDT] jtv: 2 host commands remaining this half hour.
[09-21-2017 @ 22:06:55.775 MDT] jtv: 2 host commands remaining this half hour.