Can you send us an email to melanie@vnstudioelan.com please, and reference this post in it?
Viewing post in Highway Blossoms: Next Exit comments
I also purchased the base game through JAST USA and I am also having issues getting the DLC to work. I am either getting error messages or the DLC is just not showing up. I tried installing Next Exit through the itch.io website and the launcher, but no luck. I'm not sure what I'm doing wrong. Am I just placing the DLC files into the wrong folder (I thought it would be under the "game" folder)? Do I also need to send an email to that same address?