PHP Fatal Errors

Since upgrading to 2.7.1, my site is riddled with Server Error 500. It was the only plugin I updated this am. I had to call tech support and even they couldn’t figure it out. Then I looked at the error log in the wp-admin folder, and this is what it says:

[02-Jul-2021 15:12:12 UTC] PHP Fatal error:  Uncaught Error: Cannot use object of type WP_Error as array in /…/wp-content/plugins/ad-inserter/ad-inserter.php:6032
Stack trace:
#0 /…/wp-includes/class-wp-hook.php(292): ai_ajax_backend('')
#1 /…/wp-includes/class-wp-hook.php(316): WP_Hook->apply_filters('', Array)
#2 /…/wp-includes/plugin.php(484): WP_Hook->do_action(Array)
#3 /…/wp-admin/admin-ajax.php(187): do_action('wp_ajax_ai_ajax...')
#4 {main}
  thrown in /…/wp-content/plugins/ad-inserter/ad-inserter.php on line 6032

Any help would be appreciated. Is there a way to download the previous version somewhere and/or revert back?