Error on activation

On activation got this error –

Strict Standards: call_user_func_array() expects parameter 1 to be a valid callback, non-static method allow_php_in_posts::menu_register() should not be called statically in /var/www/vhosts/landlordaccreditationscotland.com/httpdocs/wp-includes/plugin.php on line 496 Strict Standards: call_user_func_array() expects parameter 1 to be a valid callback, non-static method allow_php_in_posts::menu_register_extras() should not be called statically in /var/www/vhosts/landlordaccreditationscotland.com/httpdocs/wp-includes/plugin.php on line 496

The plugin generated 743 characters of unexpected output during activation.

https://wordpress.org/plugins/allow-php-in-posts-and-pages/