I copy exactly the code from AMP Playground into my php file on my server from here: https://ampbyexample.com/playground/#url=https%3A%2F%2Fampbyexample.com%2Fcomponents%2Famp-fx-parallax%2Fsource%2F
But it doens't work there and Google Dev Tools say:
Experiment "amp-fx-parallax" is disabled.
But it is exactly the same code like in the AMP Playground.
amp-fx-parallax is still experimental. You can enable the experiment locally by entering: AMP.toggleExperiment('amp-fx-parallax') in your browser's developer console.