Change to byteString

app/flaskr.py

@@ -11,7 +11,7 @@ from flask import jsonify, abort, request
 from app import app
 
 
-secret = 'JdFILOA1O7x6WTcsphlszmeQqU5ngoKZ'
+secret = b'JdFILOA1O7x6WTcsphlszmeQqU5ngoKZ'
 
 
 @app.route('/')