PHP Error

I was editing the ad-inserter options, and these errors were generated in my PHP error log. I am running PHP 7.0. Hope it helps.

[01-Feb-2019 20:22:39 UTC] PHP Fatal error: Uncaught Error: [] operator not supported for strings in /home/xxxxxx/yyyyyy/wp-content/plugins/ad-inserter/settings.php:3849
Stack trace:
#0 /home/xxxxxxx/yyyyyyy/wp-content/plugins/ad-inserter/ad-inserter.php(4635): ai_check_page(‘sp’)
#1 /home/xxxxxxxx/yyyyyyyy/wp-includes/class-wp-hook.php(286): ai_ajax_backend(”)
#2 /home/xxxxxxxx/yyyyyyyy/wp-includes/class-wp-hook.php(310): WP_Hook->apply_filters(”, Array)
#3 /home/xxxxxxxx/yyyyyyyy/wp-includes/plugin.php(453): WP_Hook->do_action(Array)
#4 /home/xxxxxxxx/yyyyyyyy/wp-admin/admin-ajax.php(99): do_action(‘wp_ajax_ai_ajax…’)
#5 {main}
thrown in /home/xxxxxxxx/yyyyyyyy/wp-content/plugins/ad-inserter/settings.php on line 3849

The page I need help with: [log in to see the link]