Dropbox Saver API url as base64 works when upload 1 file when upload multiple i got error?

Hello, 

i used "https://www.dropbox.com/developers/saver" Api and based on document to upload multiple file i send list of base64 string to dropbox, but i got an error fail to upload, when deselct all files and leave 1 file only it uploaded correctly ? 

and here sample code 

 var options ={files:[]};
          for (var i=0;i< attachments.length; i++) {
            var item = attachments[i];
            var file = {
              url: 'data&colon;application/pdf;base64,'+ item.fileByte
              filename: item.name
            };
            options.files.push(file);
          }

var button = window.Dropbox.createSaveButton(options);
document.getElementById("pdfcontainer").appendChild(button);