I am trying to build a Custom activity for journey builder. I was using the great tutorial by Markus Slabina Salesforce Marketing Cloud - Service Cloud Custom Split Activity as a start. The activity is hosted in Heroku as advised. The activity loads ok into journey builder, but when I try to activate I get the error "A custom activity or entry source failed validation. Check to ensure that the activity or entry source publishes to a valid endpoint."
When I check the logs in Heroku, I see "JsonWebTokenError: jwt malformed"
I can write the body to the console ok, and I have set the secret up just as the tutorial said.
Has anyone else seen this problem and can anyone point me to the up to date procedure for creating keys / salt within marketing cloud and where to use them within the Custom Activity? I believe the salesforce instructions and the tutorial instructions are out of date and this may be my problem.
Any help is greatly appreciated.