How to query API set up with Flask-restless

I'm trying to learn how to serve up data in a Flask app and mysql database both served on pythonanywhere.

I've added a route to /test with a function which is designed to connect to an existing mysql database table, and then serve it up as an API with flask-restless's create_api.

from flask.ext.sqlalchemy import SQLAlchemy
from sqlalchemy import create_engine
from sqlalchemy.orm import scoped_session, sessionmaker
from sqlalchemy.ext.declarative import declarative_base
from flask.ext.cors import CORS


app.config["SQLALCHEMY_DATABASE_URI"] = SomeLoginDetails
app.config["SQLALCHEMY_POOL_RECYCLE"] = 299

db = SQLAlchemy(app)

@app.route("/test")
def create_api():
    app.config['CORS_ALLOW_HEADERS'] = "Content-Type"
    app.config['CORS_RESOURCES'] = {r"/api/*": {"origins": "*"}}
cors = CORS()
    engine = create_engine(SomeLoginDetails)
    Base = declarative_base()
    Base.metadata.bind = engine
    class Prices(Base):
        __tablename__ = 'table'
        col1 = Column(Integer, primary_key=True)
        col2 = Column(Float)
        col3 = Column(Float)
        col4 = Column(Float)
    Base.metadata.create_all()
    manager = flask.ext.restless.APIManager(app,
                                    flask_sqlalchemy_db = db)
    manager.create_api(Prices, methods=['GET'], max_results_per_page =1000)
    return "OK"

If I leave off the last Return "OK" I get an error along the lines of:

File "/home/username/.local/lib/python2.7/site-packages/flask/app.py", line 1566, in make_response
    raise ValueError('View function did not return a response')
ValueError: View function did not return a response

However, if I add it, I receive no errors.

Why is that?

And where is the endpoint? I had tried

http://xxx-sitename-xxx.pythonanywhere.com/test/api

but I receive a Not Found page error.

For the first question:

the reason is clear, your view function should return a response, it can be a str, unicode, WSGI object or a tuple.

For the second question:

If you want to know what is endpoint in flask, you can see this question: What is an 'endpoint' in Flask?. And the reason why you get a NotFound error, is that you didn't define the /test/api route, you only have /test route.