Validation Error : Event Handler content must support atleast one class

Summary:

I am trying out Process designer and i am following the documentation https://documentation.custhelp.com/euf/assets/devdocs/cloud22c/olh/CoreFeatures/topicrefs/c_Example_object_event_handler_script_bs1140213.html

Content (required):

I am getting this error when i try to upload the same php file available in the documentation

Could someone please elaborate what the error is and how to get rid of this?

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Code Snippet (add any code snippets that support your topic, if applicable):