The thing is package details page or link template won’t show this download link to the non-members. I guess you are using this URL in a customized way.
There is still a way to redirect the user using the wpdm_download_permission_denied hook. Add the following code to your theme’s function.php file to redirect the user to the login page ( replace the your_login_url with proper url ),
add_action('wpdm_download_permission_denied', 'wpdm_permission_denied_login_redirect');
function wpdm_permission_denied_login_redirect($id){
if( !is_user_logged_in() ):
wp_redirect( "your_login_url" );
exit();
endif;
}
