graphql endpoint Method POST not allowed for URL

When I add the code shown in the example and point my browser to the URL the GraphiQL web page is displayed but an error stating Method POST not allowed for URL. I see the GET request to serve the web page for the GraphiQL UI returned successfully. I then see a POST request and the error "Method POST not allowed for URL" is returned.

After asking on the Sanic Discord support channel it was recommended that I add methods=['POST'] to the app.add_route call but this did not change the outcome.

This is running with:
sanic v21.3.4
sanic-graphql v1.1.0
graphene v2.1.8