Unable to Add Upload Mime

I have a client site where the client needs to be able to upload .dotx files. (The site is for internal company use.) We are receiving the following error when trying to upload the file:

Sorry, this file type is not permitted for security reasons.

I have added the following filter in the functions file to allow .dotx files to be uploaded:

function custom_upload_mimes ( $mime_types ) {
  $mime_types['dotx'] = 'application/vnd.openxmlformats-officedocument.wordprocessingml.template';
  return $mime_types;
}
add_filter('upload_mimes', 'custom_upload_mimes');

Unfortunately we still receive the error: Sorry, this file type is not permitted for security reasons.

The only way to successfully upload the file was to allow unfiltered uploads.

Please advise.

• This topic was modified 5 years, 9 months ago by kisabelle.