if( resp.success == true ){
  toastr.success( file.name + ' has been added.')
  fileElement.classList.add("dz-complete");

}else{
  toastr.error( 'Error:' + resp.msg);
  var fileElement = file.previewElement;
  fileElement.classList.add("dz-error");

  var errorMessageElement = fileElement.querySelector(".dz-error-message");
  if (errorMessageElement) {
    errorMessageElement.textContent = "Custom error message here";
  }
}