filesUploadSessionFinishBatchV2: Response failed with a 413 code

Hello! 

I am trying to upload 10~20 image files at once to Dropbox professional account with Javascript SDK.

Each image is less than 15MB.

According to DBX Performance guide, I tried to upload 1 image with batch function like below.

file1 = "./public/demo/1.png";
file2 = "./public/demo/2.jpg";

data1 = fs.readFileSync(file1);
data2 = fs.readFileSync(file2);

tpath1 = "/demo/data12.png";
tpath2 = "/demo/data2.jpg";

function startBatch() {   
  return new Promise(resolve=> {
    r = dbx.filesUploadSessionStartBatch({
      num_sessions: 1
    });
    resolve(r);
  });
}

function upload(sid) {
  return new Promise(resolve=> {
       // r = dbx.filesUploadSessionStart({ close: true, contents: data1})
       console.log("upload func:"+sid);


    r = dbx.filesUploadSessionAppendV2({
      contents: data1,
      cursor: {
        contents: data1,
        session_id: sid[0],
        offset: data1.length 
      },
      close: true
    });
    resolve(r);
  });  
}

(async ()=>{
  r = await startBatch();  
  sid = r.result.session_ids;
  console.log(sid);

  (async ()=>{
    r1 = await upload(sid);
    console.log(r1);
  })();

  dbx.filesUploadSessionFinishBatchV2({
    entries: [{
      cursor: {
        session_id: sid[0],
        offset: data1.length,
        contents: data1 
      },
      commit: {
        path: tpath1, 
        mode: true, 
        autorename: true,
        mute: false, 
        strict_conflict: true
      }
    }]
  })

})();

I tried to find out what the solution is, so far I don't get one.

Please note that I'm new to Javscript and ES6 : (

If you show me a code, that would be helpful.

I just want to upload 20 image files it without any error. 

Help me out please.