我仔细检查了你提供的Postman集合配置，导致请求返回"Bad Request"的核心问题很清晰：

• 请求URL缺少协议头：你写的echo.getpostman.com/post没有指定http://或https://协议前缀。HTTP客户端（包括Postman）无法识别这个地址的通信协议，服务器收到不合法的请求地址后，就会返回400 Bad Request错误。

另外，我确认了请求体的JSON转义是正确的（"{ \"data\": \"123\" }"），这部分没有问题。

下面是修正后的完整集合配置，只需要给URL加上https://前缀即可：

{
  "collection": {
    "variables": [],
    "info": {
      "name": "Sample Collection",
      "description": "This is just a sample collection.",
      "schema": "https://schema.getpostman.com/json/collection/v2.0.0/collection.json"
    },
    "item": [
      {
        "name": "This is a folder",
        "description": "",
        "item": [
          {
            "name": "Sample POST Request",
            "request": {
              "url": "https://echo.getpostman.com/post",
              "method": "POST",
              "header": [
                {
                  "key": "Content-Type",
                  "value": "application/json",
                  "description": ""
                }
              ],
              "body": {
                "mode": "raw",
                "raw": "{ \"data\": \"123\" }"
              },
              "description": "This is a sample POST Request"
            },
            "response": []
          }
        ]
      }
    ]
  }
}

把这个配置导入Postman后，重新发送请求就能正常得到Postman Echo服务的响应了。

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