Retrofit multiple file upload with progress in android

I use the library Retrofit2 to upload multiple images to the server, the code below.
I don’t understand why only 1 photo is uploaded.On the server receiver, too, only one photo.
Please tell me what is wrong with my code and how can I solve this?
The code was taken from the github from the multiboot lesson. At the first start, 4 photos were uploaded, as I chose.
And for some reason, if I select 1 photo, nothing happens.

public void Loader(){
            Intent intent = new Intent();
            intent.setType("image/*");
            intent.putExtra(Intent.EXTRA_ALLOW_MULTIPLE, true);
            intent.setAction(Intent.ACTION_GET_CONTENT);
            startActivityForResult(Intent.createChooser(intent,"Select Picture"), 1);
    }
    ArrayList<files> listUrl = new ArrayList<>();
    /**Обработчик фото*/
    @Override
    public void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);
        if(requestCode == SELECT_PICTURES) {
            if (resultCode == MainActivity.RESULT_OK) {
                if (data.getClipData() != null) {
                    int count = data.getClipData().getItemCount();
                    if(count>5){
                        count = 4;
                    }
                    image.setVisibility(GONE);
                    slider.setVisibility(VISIBLE);
                    int currentItem = 0;
                    while (currentItem < count) {
                        test.get(currentItem).setVisibility(VISIBLE);
                        Uri imageUri = data.getClipData().getItemAt(currentItem).getUri();
                        getImageFilePath(imageUri);
                        currentItem = currentItem + 1;
                    }
                }if(files.size()>0){
                    uploadFiles();
                }

            }
        }
    }
    public void getImageFilePath(Uri uri) {

        File file = new File(uri.getPath());
        String[] filePath = file.getPath().split(":");
        String image_id = filePath[filePath.length - 1];
        Cursor cursor = getContentResolver().query(android.provider.MediaStore.Images.Media.EXTERNAL_CONTENT_URI, null, MediaStore.Images.Media._ID + " = ? ", new String[]{image_id}, null);
        if (cursor!=null) {
            cursor.moveToFirst();
            String imagePath = cursor.getString(cursor.getColumnIndex(MediaStore.Images.Media.DATA));
            files.add(imagePath);
            cursor.close();
        }
    }

    public void uploadFiles(){
        File[] filesToUpload = new File[files.size()];
        for(int i=0; i< files.size(); i++){
            filesToUpload[i] = new File(files.get(i));
        }
        showProgress("Uploading media ...");
        FileUploader fileUploader = new FileUploader();
        fileUploader.uploadFiles("/", "file", filesToUpload, new FileUploader.FileUploaderCallback() {
            @Override
            public void onError() {
                hideProgress();
            }

            @Override
            public void onFinish(String[] responses) {
                hideProgress();
                for(int i=0; i< responses.length; i++){
                    String str = responses[i];
                    Log.e("RESPONSE "+i, responses[i]);
                }
            }

            @Override
            public void onProgressUpdate(int currentpercent, int totalpercent, int filenumber) {
                updateProgress(totalpercent,"Uploading file "+filenumber,"");
                Log.e("Progress Status", currentpercent+" "+totalpercent+" "+filenumber);
            }
        });
    }

    public void updateProgress(int val, String title, String msg){
        pDialog.setTitle(title);
        pDialog.setMessage(msg);
        pDialog.setProgress(val);
    }

    public void showProgress(String str){
        try{
            pDialog.setCancelable(false);
            pDialog.setTitle("Please wait");
            pDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
            pDialog.setMax(100); // Progress Dialog Max Value
            pDialog.setMessage(str);
            if (pDialog.isShowing())
                pDialog.dismiss();
            pDialog.show();
        }catch (Exception e){

        }
    }

    public void hideProgress() {
        try {
            if (pDialog.isShowing())
                pDialog.dismiss();
        } catch (Exception e) {

        }
    }