Ktor客户端，如何指定正文参数

import io.ktor.client.HttpClient
import io.ktor.client.features.json.JsonFeature
import io.ktor.client.features.json.serializer.KotlinxSerializer
import io.ktor.client.request.post
import io.ktor.http.ContentType
import io.ktor.http.contentType

suspend fun main() {
    val client = HttpClient {
        install(JsonFeature) {
            serializer = KotlinxSerializer()
        }
    }

    val requestBody = mapOf("key" to "value") // 请求的正文参数

    val response = client.post<String> {
        url("https://example.com/api/endpoint") // 请求的URL
        contentType(ContentType.Application.Json) // 指定内容类型为JSON
        body = requestBody // 设置请求的正文参数
    }

    println(response) // 处理响应结果

    client.close()
}