When you setup Slack forwarding into a private channel, Birdie won't be able to post your feedback into that channel until you add its bot into the channel.

Fixing this issue is a child game: go right into your channel, and type in @Birdie Post...... Slack will say that this user is not part of that channel and propose your to add it. Do it... and that's all. Once added to the channel, all your videos will be forwarded into Slack!