<div class="row">
    <div class="col-md-9">
        <div id="dropzone">
            <form action="/Home/Upload" class="dropzone needsclick dz-clickable" id="uploader">
                <div class="dz-message needsclick">
                    Drop files here or click to upload.<br>
                </div>
            </form>
        </div>
    </div>
</div>


<script>
    $(document).ready(function () {

        Dropzone.options.uploader = {
            paramName: "file",
            maxFilesize: 256,
            acceptedFiles: "application/zip,application/octet-stream,application/x-zip-compressed,multipart/x-zip,.zip",
            maxFiles: 1
        };

});
</script>

[HttpPost]
    public async Task<IActionResult> Upload(IFormFile file)
    {
        var uploads = Path.Combine(_environment.ContentRootPath, "Uploads");
        if (file.Length > 0)
        {
            using (var fileStream = new FileStream(Path.Combine(uploads, file.FileName), FileMode.Create))
            {
                await file.CopyToAsync(fileStream);
            }
        }
        return RedirectToAction("Index");
    }

Dropzone.options.myAwesomeDropzone = {
  accept: function(file, done) {
    if (file.name.endsWith !== ".zip") {
      done("Naha, you don't.");
    }
    else { done(); }
  }
};