Wanderlust exercise & Foursquare

I’m on the wanderlust exercise (link below) and when I get to the point 14: “Copy and paste the URL into a new tab in your browser.” I get this answer in the browser:
“{“meta”:{“code”:400,“errorType”:“invalid_auth”,“errorDetail”:“Missing access credentials. See https://developer.foursquare.com/docs/api/configuration/authentication for details.”,“requestId”:“5d386ea19df1dc0023681f03”},“response”:{}}”

Of course it something going on with credentials but I don’t know how to solve them.