Hi, the trigger for lambda function is not applied to lambda alias. So basically you have to create a new trigger for every single alias.
For example if you your lambda name Alexa and your alias is Dev. On lambda console, access to LambdaFunctions > Alexa > Dev then add trigger to Alexa Skill Set and click "Save" . After that go to Alexa developer console and modify arn to add ":dev" at the end i.e. arn:aws:lambda:us-east-1:xxxxxxx:function:Alexa:dev