I am starting to build my web service to integrate with Amazon Echo Dot (Alexa Skills Kit). I intend to use smart home skills using a Lambda adapter that will eventually connect to my web service. In order to use this, I would of course need to authorize Alexa with my server via OAuth2.
The problem I have is that Amazon seems to be rejecting my StartSSL class 1 certificate. Alexa app successfully calls my login page where I input my user name and password. I then redirect back to Amazon passing back the code. I can then see Amazon calling my service (via WireShark) but it eventually fails with error 46 - invalid certificate (just to be clear - this message is issued by Amazon). I've run multiple SSL checks online and they all show that my certificate and set up are valid. I also checked the list of Amazon certified CAs and StartSSL is on the list.
Any help on this would be much appreciated.