Bamboo webhook success but Bitbucket Cloud logs 401 error

[ncapp]

I've created a Bamboo webhook to accept trigger requests for a Bitbucket Cloud repository.

The webhook works fine, when I push code changes to Bitbucket the Bamboo build is automatically triggered.

Bamboo knows that the trigger request is from my Bitbucket Cloud user.

One strange thing is that Bitbucket Cloud logs a 401 error response for the trigger request, even though it has succeeded?

I should add I'm externally exposing my Bamboo app, listening on localhost, via the ngrok redirection tool.