allow File field to upload .json to specific directory

I've working on a post meta that I need to upload a .json file to a specific directory under wp-content. In my testing I see that I can upload PDF or image files, but not .json.

I've added a mime types filter - but the file is still not uploading.

add_filter( 'upload_mimes', 'my_myme_types', 1, 1 );
function my_myme_types( $mime_types ) {
  $mime_types['json'] = 'application/json'; // Adding .json extension
  return $mime_types;
}

Thank you.