Token Mismatch when uploading big files using laravel file manager

I'm using Laravel5.1 and tinyMCE with laravel file manager (unisharp) and I'm always getting this error when I'm uploading big files (e.g. 20MB and up). I've searched about it on internet but I didn't find something similar with my problem. Please see my code for your review.

Code:

<div class="input-group">
    <input type="text" name="file_path" id="file_path" class="form-control" value="" readonly>
    <a id="lfm" class="input-group-addon btn btn-primary" data-input="file_path">
        <i class="fa fa-file"></i> Choose file...
    </a>
</div>

Script:

<script>
    getTiny('', 'textarea'); // customized function for tinyMCE
    {!! \File::get(base_path('vendor/unisharp/laravel-filemanager/public/js/lfm.js')) !!}
    var domain = "/laravel-filemanager";
    $('#lfm').filemanager('file', {prefix: domain});
</script>

via Chebli Mohamed