why select schema not working?

"platform ": {
            "title": "Search engine",
            "type": "string",
            "description": "Select the search engine you want your websites from.",
            "editor": "select",
            "default": "Duckduckgo",
            "enum": ["ddg", "ggl", "serp"],
            "enumTitles": ["Duckduckgo", "Google", "Serpapi"]
            },

I have this in my actor's input schema. Then I get the content of this
 actor_input = await Actor.get_input() or {}
            raw_query = actor_input.get('query')
            query = raw_query.replace(" ", "+")
            numbers_of_results = actor_input.get('results')
            engine = actor_input.get('platform')

but when I print the engine's content, it says
None
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why select schema not working? - Apify & Crawlee