Can't read Json in WPF

I don't think I understand this error. It requires an array? but how? Should I make a loop?
        static List<Persondata> persondata()
        {
            string fileName = @"C:\Users\elko\source\repos\JsonData\JsonData\bin\Debug\net6.0-windows\Persons.json";
            if (File.Exists(fileName))
            {
                var persons = JsonConvert.DeserializeObject<List<Persondata>>
                (File.ReadAllText(fileName));

                return persons;
            }
            return null;
        }
    }
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