angularjs - k-file-error when kendo upload is successfull -

i manage upload files kendo , angularjs, files remain red , have k-file-error class, files uploaded , can have them on back. why there error ? please me ?

<div class="demo-section k-content">         <div>             <h4>upload files</h4>             <div class="dropzoneelement">drag , drop file here</div>             <input name="files"               ng-model="vm.files"               type="file"               kendo-upload               k-async="{ saveurl: 'http://localhost:5000/api/upload/', removeurl: 'remove', autoupload: true, withcredentials: false }"               k-select="onselect"               k-upload="onupload"               k-progress="onprogress"               k-success="onsuccess"               options="vm.options"               />         </div>         <button ng-click="vm.test()">test</button>     </div>  class documentcontroller {   /* @nginject */   constructor($scope, authtokenservice) {     this.name = 'document';     $scope.onselect = e => {       // console.log(e.files);     };     $scope.onupload = e => {       const token = authtokenservice.gettoken();       // check if token expire       if (token && authtokenservice.isexpired(token)) {         authtokenservice.settoken();       }       const xhr = e.xmlhttprequest;       if (xhr) {         xhr.addeventlistener('readystatechange', () => {           if (xhr.readystate === 1) {             // add token header             if (token) {               xhr.setrequestheader('authorization', `bearer ${token}`);             }           }         });       }     };     $scope.onsuccess = e => {       console.log(e);     };     $scope.onprogress = e => {       // console.log(e);     };     this.options = {       dropzone: '.dropzoneelement'     };   } }  export default documentcontroller; 

you should return valid json result server response. return json(true) should work.