I am glad that worked for you. I too struggled with that for days!!! But then once I shut off IPV6 on my router “boom” it all worked. 
As to your Webcore, I think it may be your POST request. I installed the following “SmartApp” and “Device Handler” from here: [RELEASE] Google Assistant Relay SmartApp and Device Handler
then setup my webcore like this screen shot. Hope this helps.