many notices version 6.4.8

Please correct this in one of the next versions 🙂
thanks in advanced!

Notice: Undefined variable: id in
/xxx/subscribe-to-double-opt-in-comments/subscribe-to-doi-comments.php
on line 541

Notice: wpdb::escape ist seit Version 3.6 veraltet!
Benutze stattdessen wpdb::prepare() or esc_sql(). in /xxx/wp-includes/functions.php
on line 3391

Notice: Undefined index: subscribe in
/xxx/subscribe-to-double-opt-in-comments/subscribe-to-doi-comments.php
on line 549

Notice: get_settings ist seit Version 2.1 veraltet! Benutze stattdessen get_option().
in /xxx/wp-includes/functions.php on line 3391

Notice: Undefined offset: 2048 in
/xxx/subscribe-to-double-opt-in-comments/subscribe-to-doi-comments.php
on line 454

Warning: Cannot modify header information – headers already sent by
(output started at
/xxx/subscribe-to-double-opt-in-comments/subscribe-to-doi-comments.php:541) in
/xxx/wp-includes/pluggable.php on line 1196

https://wordpress.org/plugins/subscribe-to-double-opt-in-comments/