If you do not have your own api token, you are using the global project that google provides for anonymous testing. This may mean that someone else testing is using the 240 tokens/minute allocated to the test google project.

Simply create a google api token in your developers console for the pageSpeed API. This will also turn the service on.

The below link will get you started

https://developers.google.com/speed/docs/insights/v5/get-started