Alexa Skills Integration

I'm trying to bring my finished voiceflow project into Alexa Skills. I've followed this (https://xavidop.me/alexa/2023-11-21-voiceflow-alexa/) tutorial, and my project does not seem to work fully in Alexa skills -- there are certain instances where Alexa skills says "undefined" in place of a variable that was kept track of in Voiceflow. Any ideas on why this may be happening? There are other variables in my project that are working fine and were said by the assistant on both voiceflow and Alexa Skills.