rasa: "Wrong fb secret!" - How to configure the Facebook Connector correctly? - Python 3 only

Rasa Core version: rasa-core (0.8.0a4, /root/rasa_core) including pull request #160

Python version: Python 3.6.3 |Anaconda, Inc.

Operating system : Ubuntu 16.04.3

Issue:

I have a problem with connection the FB Messenger. I have included pull request #160 and also tried it with the old dependency pymessenger and with my workaround here is supposed in Bug #153

I get the errormessage:

2018-01-08 12:13:06 WARNING  rasa_core.channels.facebook - Invalid fb verify token! Make sure this matches your webhook settings on the facebook app.
127.0.0.1 - - [2018-01-08 12:13:06] "GET /webhook?hub.mode=subscribe&hub.challenge=246570936&hub.verify_token=my-rasa-testbot HTTP/1.0" 200 157 0.001802
2465709362018-01-08 

if i run

python -m rasa_core.run -d models/dialogue -u models/nlu/current    --port 5002 --connector facebook --credentials credentials.yml

and send a message (as an owner) to my Bot.

The webhook looks like it is correctly installed: I connect to my bot via an nginx proxy server with an Let’s encrypt cert installed.

In the credentials.yml I use the secret from here. Is this correct?

What else can I try?