Unable Connecting Power BI to Hadoop HDFS failed to get contents

When I'm trying to connect Power BI to Hadoop webhdfs, i get this error

DataSource.Error: HDFS failed to get contents from 'http://xxx.xx.x.x:50070/webhdfs/v1/myFolder/20200626150740_PERSONAL_IDS'. Status code: 503, description: 'Service Unavailable'.

When I access the URL, error like this occurs:

{
  RemoteException: {
    exception: "UnsupportedOperationException",
    javaClassName: "java.lang.UnsupportedOperationException",
    message: "op=NULL is not supported"
  }
}

Anyone can help this out?

An operation (?op=...) is required when you use webhdfs REST API with http(s): scheme.

For example, when I type this in my browser:

https://<my.namenode.host>:9871/webhdfs/v1/user?op=LISTSTATUS

... I get back the list of hdfs directory /user content (similar to what I'll get with hadoop fs -ls /user plus some additional info):

// 20200709155934
// https://<my.namenode.host>:9871/webhdfs/v1/user?op=LISTSTATUS

{
  "FileStatuses": {
    "FileStatus": [
      {
        "accessTime": 0,
        "blockSize": 0,
        "childrenNum": 2,
        "fileId": 56899,
        "group": "supergroup",
        "length": 0,
        "modificationTime": 1592790690971,
        "owner": "hdfs",
        "pathSuffix": "hdfs",
        "permission": "700",
        "replication": 0,
        "storagePolicy": 0,
        "type": "DIRECTORY"
      },
      . . . . 
      {
        "accessTime": 0,
        "blockSize": 0,
        "childrenNum": 2,
        "fileId": 16390,
        "group": "hive",
        "length": 0,
        "modificationTime": 1591715444764,
        "owner": "hive",
        "pathSuffix": "hive",
        "permission": "1775",
        "replication": 0,
        "storagePolicy": 0,
        "type": "DIRECTORY"
      },
      . . . . 
      {
        "accessTime": 0,
        "blockSize": 0,
        "childrenNum": 2,
        "fileId": 16454,
        "group": "mazaneicha",
        "length": 0,
        "modificationTime": 1591035918913,
        "owner": "mazaneicha",
        "pathSuffix": "mazaneicha",
        "permission": "720",
        "replication": 0,
        "storagePolicy": 0,
        "type": "DIRECTORY"
      },
      . . . .
    ]
  }
}

You can find the complete list of REST API operations online.