[LINE Message API / Laravel] メッセージが送信できない。

前提・実現したいこと

ボットから応答メッセージを行いたいのですが、メッセージを送信することができません。

https://developers.line.biz/ja/reference/messaging-api/#send-reply-message

AuthorizationやreplyTokenが間違っていないことは確認しています。

使用パッケージ

guzzle

エラー内容

**「リクエストボディがJSONとして解析できません」**というエラー内容が返ってきました。

local.ERROR: Client error: `POST https://api.line.me/v2/bot/message/reply` resulted in a `400 Bad Request` response:
{"message":"The request body could not be parsed as JSON (line: 1, column: 12)"}
 {"exception":"[object] (GuzzleHttp\Exception\ClientException(code: 400): Client error: `POST https://api.line.me/v2/bot/message/reply` resulted in a `400 Bad Request` response:
{\"message\":\"The request body could not be parsed as JSON (line: 1, column: 12)\"}
 at /laravel/vendor/guzzlehttp/guzzle/src/Exception/RequestException.php:113)
"}

コード

<?php
// logs
use Illuminate\Support\Facades\Log;
// Guzzle
use GuzzleHttp\Client;

$messages = json_encode([
  "type" => "flex",
  "altText" => "This is a Flex Message",
  "contents" => [
    "type" => "bubble",
    "body" => [
      "type" => "box",
      "layout" => "horizontal",
      "contents" => [
        [
          "type" => "text",
          "text" => "Hello,"
        ],
        [
          "type" => "text",
          "text" => "World!"
        ]
      ]
    ]
  ]
]);

Log::info($messages);

//guzzle
$line_url = "https://api.line.me/v2/bot/message/reply";
$client = new Client();
$options = [
  "headers" => [
    "Content-Type" => "application/json",
    "Authorization" => "Bearer " . $channelAccessToken,
  ],
  "form_params" => [
    "replyToken" => $replyToken,
    "messages" => $messages
  ]
];
Log::info($options);

$client->request(
  "POST",
  $line_url,
  $options
);

ログ

JSONになっているか確認するためログを使いました。

$messages

問題なくJSONになっていました。

{
  "type": "flex",
  "altText": "This is a Flex Message",
  "contents": {
    "type": "bubble",
    "body": {
      "type": "box",
      "layout": "horizontal",
      "contents": [
        { "type": "text", "text": "Hello," },
        { "type": "text", "text": "World!" }
      ]
    }
  }
}

$options

array (
  'headers' => 
  array (
    'Content-Type' => 'application/json',
    'Authorization' => 'Bearer zTon3fKIG7m7dH1/AnyA/~~,
  ),
  'form_params' => 
  array (
    'replyToken' => '16bc990fb7ab46028cbceb00000000',
    'messages' => '{"type":"flex","altText":"This is a Flex Message","contents":{"type":"bubble","body":{"type":"box","layout":"horizontal","contents":[{"type":"text","text":"Hello,"},{"type":"text","text":"World!"}]}}}',
  ),
)

curlの場合

curlの場合、replyTokenが使えないため、応答メッセージではなくプッシュメッセージになりますがこちらでも試してみました。
https://developers.line.biz/ja/reference/messaging-api/#send-push-message

結果は正しく送信することができました。
コードは以下の通りです。

curl -v -X POST https://api.line.me/v2/bot/message/push \
-H "Content-Type: application/json" \
-H "Authorization: Bearer zTon3fKIG7m7dH1/AnyA/~~ \
-d '{
  "to": "Udf9ab83bf44a25cd9a90f000000000",
  "messages":[
    {"type":"flex","altText":"This is a Flex Message","contents":{"type":"bubble","body":{"type":"box","layout":"horizontal","contents":[{"type":"text","text":"Hello,"},{"type":"text","text":"World!"}]}}}
  ]
}'