Swift中如何将字典数组转换为可用JSON对象？

我在创建嵌入字典数组的JSON对象时遇到问题，以下是尝试的错误代码，其中parameters中的myMessages会报错：

let myMessages: [Dictionary: Any?] = [
    { role: "system", content: "You’re a social media manager writing Instagram captions." },
    { role: "user", content: "I want to post something on Instagram on Mother’s day. Brainstorm some ideas." },
]
 
let parameters: [String: Any?] = [
    "model": model,
    "messages": myMessages,
]
guard let parametersJson = try? JSONSerialization.data(withJSONObject: parameters, options: .prettyPrinted) else { 
    return
}

编辑1：
如果将myMessages改为如下字典形式，代码可以编译运行，但API要求传入数组：

var myMessages = ["role": "user", "content": "How many days in a week"]

编辑2：
参考已采纳的答案及下方评论，以下代码可正常运行。问题点包括：

• 数组的正确声明方式为[[String: Any?]]
• Swift中不能使用大括号{}定义字典，需改用方括号[]
• 字符串类型的键需要加引号

var myMessages: [[String: Any?]] = [
            [ "role": "system", "content": "You love pizza." ],
            [ "role": "user", "content": "What do you think of pizza" ]
        ]

内容的提问来源于stack exchange，提问作者user6631314