unauthorized token callback failed to load .... server status 500

i need to add an authentication systen in web app and i choosed auth0.
i worked with it one year ago and everything was ok and i liked it. but there was a separation between backend code and front end code where i customize the lock widgets in html inside
but now i found out that alot has changed and i couldnt figure out a way to make it work even with the code u provided in github it didnt work after i create account and i authenticate it returnes : => callback Failed to load resource: the server responded with a status of 500

here is the code (Ofc i changed my auth information) => auth0-nodejs-webapp-sample/01-Login at master · auth0-samples/auth0-nodejs-webapp-sample · GitHub

after loging in i get an internal server error AND UNAUTHORIZED TOKEN … any help please ? and one other question … how to customize the widgets now …