Feature Request : Incoming webhook to all teams with team and channel specified in payload?

Hi there!
I was testing this, overriding the channel, and I get errors all the time. If I put a channel name, I get error 500 response or if I try to make it with a user @somename (valid user) I also get an error 500 response. Only when the channel property is not included the webhook succeeds. Even putting the same channel as the webhook when created, still fails.
Is there a special format to put the channel name? with some # or some other character?
I'm trying to make a webhook that will send messages and it can vary, sometimes it will send to users, sometimes to channels.
Based on the documentation, this should be possible, but I can't get it to work.
I've tested it from Firefox using developer tools and posting.