Hi,
Looking into the error with 400 error, I think when Google made a callback to your server, it can't see your server "Up". You will need to check your server name or port setup, etc... It is better if you can give me an instruction what you did and setup for your machine/folders/file. And then I can reproduce it under my local lab. After I can have my lab as the same yours, I can test and fix it before give your a guideline to figure out your issue completely.
Regards,
--T