We are building a custom Alexa skill with account linking. The Account Linking flow were success on Alexa App with my account, it shows the account was "Linked". However, the accessToken is "undefined" in Lambda handler. From the cloudwatch log, there is no accessToken field exist at from handlerInput.requestEnvelope.context.System.user at all.
Same result for testing both from "Alexa Developer Console" and "Alexa App" on iOS.
Appreciate anybody could shed some light about what possibly wrong and how to chase further with root cause.