Welcome to this beautiful app.
Try calling it:
curl -H "Content-Type: application/json" -X POST -d "[{"x1":5.1, "x2":3.5, "x3":1.4, "x4":0.2}]" https://larsk-flask.herokuapp.com/predict/
curl -H "Content-Type: application/json" -X POST -d "[{"x1":5.1, "x2":3.5, "x3":1.4, "x4":0.2}, {"x1":6.2, "x2":3.4, "x3":5.4, "x4":2.3}]" https://larsk-flask.herokuapp.com/predict/
blaaah