I just installed this plugin – while it seemed perfect to me, I ran accros this error trying to add a subscription to your site :

PHP Fatal error: Uncaught ArgumentCountError: Too few arguments
to function yarns_reader_new_subscription(), 1 passed in
/srv/data/web/vhosts/mysite/htdocs/wp-includes/class-wp-hook.php on line
286 and exactly 4 expected in
/srv/data/web/vhosts/mysite/htdocs/wp-content/plugins/yarns-indie-reader-master/yarns_reader.php:790

Please let me know if you need more info.