Use this example to make a protected file URL work from an email for a user that isn't logged in.

add_filter( 'frm_check_file_referer', '__return_false' );

A protected file cannot be added to Google Drive because the request from Zapier fails the referer check. Use this example to turn off the referer check whenever Zapier is making a request.

add_filter( 'frm_check_file_referer', 'turnoff_file_referer_check_for_zapier' );
function turnoff_file_referer_check_for_zapier( $check_referer ) {
	if ( ! $check_referer ) {
		return false;
	}
	return FrmAppHelper::get_server_value( 'HTTP_USER_AGENT' ) !== 'Zapier';
}