How to connect external worker?

[baccenfutter]

After fresh installation, I go into Administration->Workers and create a new worker.

• I select Worker (a worker running on another host)
• basename: foo
• password: secret
• count: 2
• I see two workers created but not connected (foo_1 and foo_2)
• I go into a server shell and create and start a worker

buildbot-worker create-worker foo_1 my-buildbot-travis-url foo_1 secret
buildbot-worker start foo_1

... and get:

2018-04-10 22:04:35+0200 [HangCheckProtocol,client] While trying to connect:
        Traceback from remote host -- exceptions.RuntimeError: rejecting duplicate worker

So, how do I connect an external worker to buildbot-travis?

[baccenfutter]

If I leave the worker count at 1, then only one worker is created and that connects perfectly fine with username foo. As soon as I raise the count >1 I run into the error.