I'm trying out the Business Chat sandbox. It seems to work OK but I can't get the package delivery demo iMessage app (https://developer.apple.com/sample-code/wwdc/2017/iMessage-Business-Chat.zip) to work right. I followed the directions about replacing <team-identifier> with my own team ID, and I have the extension on my test device. But when I send through the sandbox, no message appears on the iOS device.
I suspect it's a bug in the current beta because the "WWDC Goodies" text appears in the message list on the left in Messages, but no actual message appears in the transcript. But this is all new enough that I'm not sure if I missed a step.